U.S. patent application number 11/354924 was filed with the patent office on 2006-09-28 for electro-optical device and circuit for driving electro-optical device.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Kiyoaki Murai.
Application Number | 20060214897 11/354924 |
Document ID | / |
Family ID | 37034686 |
Filed Date | 2006-09-28 |
United States Patent
Application |
20060214897 |
Kind Code |
A1 |
Murai; Kiyoaki |
September 28, 2006 |
Electro-optical device and circuit for driving electro-optical
device
Abstract
An electro-optical device drives a plurality of pixels to
represent gray scale levels based on effective voltages by dividing
one frame into a plurality of fields, and includes a calculating
unit that receives image data specifying gray scale values in each
frame for each pixel and obtains the amount of variation of a
voltage to be applied to the pixel over adjacent frames; a
discriminating unit that discriminates whether or not the amount of
variation of the voltage satisfies a predetermined condition; a
voltage pattern determining unit that determines to supply a first
effective voltage shifted in a variation direction, rather than a
voltage according to a gray scale value specified in the image data
of a later frame of the adjacent frames, in a previous field of the
plurality of fields in the later frame, while determining to supply
a second effective voltage shifted in a direction opposite to the
variation direction, rather than the voltage according to the gray
scale value specified in the image data of the later frame, in a
later field of the plurality of fields in the later frame, for the
pixel, when it is discriminated in the discriminating unit that the
predetermined condition is satisfied; and a driving circuit that
supplies the first and second effective voltages determined in the
voltage pattern determining unit in each field of the later frame
for each pixel.
Inventors: |
Murai; Kiyoaki;
(Matsumoto-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
SEIKO EPSON CORPORATION
TOKYO
JP
|
Family ID: |
37034686 |
Appl. No.: |
11/354924 |
Filed: |
February 16, 2006 |
Current U.S.
Class: |
345/89 |
Current CPC
Class: |
G09G 3/3648 20130101;
G09G 2320/0252 20130101; G09G 3/2025 20130101; G09G 3/367 20130101;
G09G 3/2011 20130101; G09G 3/2081 20130101; G09G 3/2014 20130101;
G09G 2340/16 20130101 |
Class at
Publication: |
345/089 |
International
Class: |
G09G 3/36 20060101
G09G003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2005 |
JP |
2005-083382 |
Sep 21, 2005 |
JP |
2005-273405 |
Claims
1. An electro-optical device which drives a plurality of pixels to
represent gray scale levels based on effective voltages by dividing
one frame into a plurality of fields, comprising: a calculating
unit that receives image data specifying gray scale values in each
frame for each pixel and that calculates the amount of variation in
voltage to be applied to the pixel between temporally adjacent
frames; a judgement unit that judges whether or not the amount of
variation in voltage satisfies a predetermined condition; a voltage
pattern determining unit that, when the judgement unit judges that
the predetermined condition is satisfied, determines for the pixel:
a first effective voltage in an early field of the plurality of
fields in a later frame of the temporally adjacent frames, the
first effective voltage being shifted in a variation direction from
a voltage according to a gray scale value specified in the image
data of the later frame; and a second effective voltage in a later
field of the plurality of fields in the later frame, the second
effective voltage being shifted in a direction opposite to the
variation direction from the voltage according to the gray scale
value specified in the image data of the later frame; and a driving
circuit that supplies the first and second effective voltages in
fields of the later frame for each pixel.
2. The electro-optical device according to claim 1, wherein the
voltage pattern determining unit determines the first and second
effective voltages so that an average of a first gray scale value
corresponding to the first effective voltage and a second gray
scale value corresponding to the second effective voltage matches
the gray scale value specified in the image data of the later frame
of the temporally adjacent frames.
3. The electro-optical device according to claim 1, wherein the
predetermined condition in the judgement unit is that the amount of
variation of the voltage is not 0.
4. The electro-optical device according to claim 1, wherein the
predetermined condition in the judgement unit is that the amount of
variation of the voltage exceeds a predetermined threshold.
5. The electro-optical device according to claim 1, wherein the
voltage supplied to the pixel is specified to a positive polarity
or a negative polarity with a predetermined potential as a
reference, and the predetermined condition in the judgement unit is
that the polarity is reversed between the adjacent frames.
6. The electro-optical device according to claim 1, wherein the
voltage pattern determining unit includes: a voltage pattern
storing unit that stores voltage patterns including the first and
second effective voltages in advance; and a voltage pattern
selecting unit that selects a voltage pattern corresponding to the
amount of variation in voltage and the gray scale value specified
in the image data from the voltage patterns stored in the voltage
pattern storing unit, and the first and second effective voltages
are determined based on the selected voltage pattern.
7. The electro-optical device according to claim 1, wherein the
first and second effective voltages are voltage signals according
to gray scale values, which are symmetrical with respect to the
gray scale value specified in the image data.
8. The electro-optical device according to claim 1, wherein the
first and second effective voltages are pulse signals which have a
pulse width according to gray scale values, which are symmetrical
with respect to the gray scale value specified in the image
data.
9. An electro-optical device which drives a plurality of pixels to
represent gray scale levels based on effective voltages by dividing
one frame into a plurality of fields, comprising: a calculating
unit that receives image data specifying gray scale values in each
frame for each pixel and that obtains calculates the amount of
variation in voltage to be applied to the pixel between temporally
adjacent frames; a judgement unit that judges whether or not the
amount of variation in voltage satisfies a predetermined condition;
a voltage pattern determining unit that, when the judgement unit
judges that the predetermined condition is satisfied, determines
for the pixel: a first effective voltage in an early field of the
plurality of fields in a previous frame of the temporally adjacent
frames, the first effective voltage being shifted in a direction
opposite to a variation direction from a voltage according to a
gray scale value specified in the image data of the previous frame;
and a second effective voltage in a later field of the plurality of
fields in the previous frame, the second effective voltage being
shifted in the variation direction from the voltage according to
the gray scale value specified in the image data of the previous
frame,; and a driving circuit that supplies the first and second
effective voltages in each fields of the previous frame for each
pixel.
10. A circuit for driving an electro-optical device which drives a
plurality of pixels to represent gray scale levels based on
effective voltages by dividing one frame into a plurality of
fields, comprising: a calculating unit that receives image data
specifying gray scale values in each frame for each pixel and that
calculates the amount of variation in voltage to be applied to the
pixel between temporally adjacent frames; a judgement unit that
judges whether or not the amount of variation in voltage satisfies
a predetermined condition; a voltage pattern determining unit that,
when the judgement unit judges that the predetermined condition is
satisfied, determines for the pixel: a first effective voltage in
an early field of the plurality of fields in a later frame of the
temporally adjacent frames, the first effective voltage being
shifted in a variation direction from a voltage according to a gray
scale value specified in the image data of the later frame; and a
second effective voltage in a later field of the plurality of
fields in the later frame, the second effective voltage being
shifted in a direction opposite to the variation direction from the
voltage according to the gray scale value specified in the image
data of the later frame; and a driving circuit that supplies the
first and second effective voltages in fields of the later frame
for each pixel.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a technique for improving
display responsiveness in an electro-optical device.
[0003] 2. Related Art
[0004] For an electro-optical device such as a liquid crystal
display panel, there has been suggested a technique of suppressing
display flickers while representing halftones using a pseudo value
by periodically outputting different driving voltages for each
frame, for example, in order to increase gray scale levels over the
value of driving voltages (referred to as JP-A-2-127618).
[0005] However, in the above-mentioned technique, in some cases, a
response speed of the liquid crystal display panel may be delayed
depending on gray scale levels to be represented. For example, when
gray scale levels, which are greatly different from gray scale
levels of previous frames, are represented, in some cases, there is
a phenomenon in that previously displayed images seem to remain
behind. The a phenomenon is generated due to a low response speed
of liquid crystal material in the liquid crystal display panel.
SUMMARY
[0006] An advantage of some aspects of the invention is that it
provides an electro-optical device, a circuit for driving the
electro-optical device, and a method of driving the electro-optical
device, which is capable of improving display responsiveness while
increasing representable gray scale levels when electro-optical
material having slow optical responsiveness, such as liquid
crystal, is used to display images.
[0007] An electro-optical device according to an aspect of the
invention drives a plurality of pixels to represent gray scale
levels based on effective voltages by dividing one frame into a
plurality of fields, and includes a calculating unit that receives
image data specifying gray scale values in each frame for each
pixel and obtains the amount of variation of a voltage to be
applied to the pixel over adjacent frames, a discriminating unit
that discriminates whether or not the amount of variation of the
voltage satisfies a predetermined condition; a voltage pattern
determining unit that determines to supply a first effective
voltage shifted in a variation direction, rather than a voltage
according to a gray scale value specified in the image data of a
later frame of the adjacent frames, in a previous field of the
plurality of fields in the later frame, while determining to supply
a second effective voltage shifted in a direction opposite to the
variation direction, rather than the voltage according to the gray
scale value specified in the image data of the later frame, in a
later field of the plurality of fields in the later frame, for the
pixel, when it is discriminated in the discriminating unit that the
predetermined condition is satisfied, and a driving circuit that
supplies the first and second effective voltages determined in the
voltage pattern determining unit in each field of the later frame
for each pixel. According to the invention, it is possible to
increase a display response speed.
[0008] Preferably, the voltage pattern determining unit determines
the first and second effective voltages such that the gray scale
value specified in the image data of the later frame of the
adjacent frames in a time manner becomes an average of a first gray
scale value corresponding to the first effective voltage and a
second gray scale value corresponding to the second effective
voltage. With this configuration, it is possible to increase
representable gray scale levels.
[0009] Preferably, the predetermined condition in the
discriminating unit is, first, that the amount of variation of the
voltage is not 0, second, that the amount of variation of the
voltage exceeds a predetermined threshold, and third, when the
voltage supplied to the pixel is specified by a positive polarity
and a negative polarity with a predetermined potential as a
reference, that the polarity is reversed over the adjacent
frames.
[0010] Preferably, the voltage pattern determining unit includes a
voltage pattern storing unit that stores voltage patterns including
the first and second effective voltages in advance, and a voltage
pattern selecting unit that selects a voltage pattern corresponding
to the amount of variation of the voltage and the gray scale value
specified in the image data from the voltage patterns stored in the
voltage pattern storing unit. The first and second effective
voltages are determined based on the selected voltage pattern.
[0011] Preferably, the first and second effective voltages are
voltage signals according to the first and second gray scale
values, which are symmetrical with respect to the gray scale value
specified in the image data, or pulse signals each having a pulse
width according to the gray scale values, which are symmetrical
with respect to the gray scale value specified in the image
data.
[0012] To achieve the above advantage, the present invention also
provides an electro-optical device for driving a plurality of
pixels to represent gray scale levels based on effective voltages,
with one frame divided into a plurality of fields, including a
calculating unit that receives image data specifying gray scale
values in each frame for each pixel and obtains the amount of
variation of a voltage to be applied to the pixel over adjacent
frames; a discriminating unit that discriminates whether or not the
amount of variation of the voltage satisfies a predetermined
condition; a voltage pattern determining unit that determines to
supply a first effective voltage shifted in a direction opposite to
a variation direction, rather than a voltage according to a gray
scale value specified in the image data of a previous frame of the
adjacent frames, in a previous field of the plurality of fields in
the previous frame, while determining to supply a second effective
voltage shifted in the variation direction, rather than the voltage
according to the gray scale value specified in the image data of
the previous frame, in a later field of the plurality of fields in
the previous frame, for the pixel, when it is discriminated in the
discriminating unit that the predetermined condition is satisfied,
and a driving circuit that supplies the first and second effective
voltages determined in the voltage pattern determining unit in each
field of the previous frame for each pixel.
[0013] Further, in addition to the electro-optical device, the
present invention provides a circuit for driving the
electro-optical device and a method of driving the electro-optical
device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0015] FIG. 1 is a schematic view illustrating configuration of a
liquid crystal display device according to a first embodiment of
the invention.
[0016] FIG. 2A is a view illustrating configuration of pixels in
the liquid crystal display device.
[0017] FIG. 2B is a view illustrating configuration of pixels in
the liquid crystal display device.
[0018] FIG. 3 is a view illustrating an example of voltage
waveforms for scan lines in the liquid crystal display device.
[0019] FIG. 4 is a view illustrating configuration of a data
processing circuit in the liquid crystal display device.
[0020] FIG. 5 is a view illustrating operation of a voltage
determining unit in the data processing circuit.
[0021] FIG. 6 is a view illustrating relationship between gray
scale voltages in the liquid crystal display device.
[0022] FIG. 7A is a view illustrating variation of gray scale
voltages in the liquid crystal display device.
[0023] FIG. 7B is a view illustrating variation of gray scale
voltages in the liquid crystal display device.
[0024] FIG. 8A is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0025] FIG. 8B is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0026] FIG. 9A is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0027] FIG. 9B is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0028] FIG. 10A is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0029] FIG. 10B is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0030] FIG. 11 is a view illustrating an example of gray scale
voltages determined in the liquid crystal display device.
[0031] FIG. 12 is a view illustrating an example of voltage
waveforms for scan lines in the liquid crystal display device.
[0032] FIG. 13 is a view illustrating configuration of a data
processing circuit according to a second embodiment of the
invention.
[0033] FIG. 14 is a view illustrating a voltage pattern stored in
the data processing circuit.
[0034] FIG. 15 is a view illustrating an example of voltage
waveforms of scan lines in a liquid crystal display device
according to a third embodiment of the present invention.
[0035] FIG. 16 is a view illustrating an example of a gray scale
display in the liquid crystal display device.
[0036] FIG. 17A is a view illustrating a voltage pattern used in
the liquid crystal display device.
[0037] FIG. 17B is a view illustrating a voltage pattern used in
the liquid crystal display device.
[0038] FIG. 17C is a view illustrating a voltage pattern used in
the liquid crystal display device.
[0039] FIG. 18A is a view illustrating variations of a gray scale
value and a gray scale voltage in the liquid crystal display
device.
[0040] FIG. 18B is a view illustrating variations of a gray scale
voltage and a gray scale voltage in the liquid crystal display
device.
[0041] FIG. 19A is a view illustrating variations of a gray scale
value and a gray scale voltage in the liquid crystal display
device.
[0042] FIG. 19B is a view illustrating variations of a gray scale
voltage and a gray scale voltage in the liquid crystal display
device.
[0043] FIG. 20 is a view illustrating an example of voltage
waveforms for scan lines in the liquid crystal display device.
[0044] FIG. 21A is a view illustrating variations of a gray scale
value in a liquid crystal display device according to a fourth
embodiment of the present invention.
[0045] FIG. 21B is a view illustrating variations of a gray scale
voltage in a liquid crystal display device according to a fourth
embodiment of the present invention.
[0046] FIG. 22A is a view illustrating variations of a gray scale
value in the liquid crystal display device.
[0047] FIG. 22B is a view illustrating variations of a gray scale
voltage in the liquid crystal display device.
[0048] FIG. 23A is a view illustrating variations of a gray scale
value a liquid crystal display device according to a fifth
embodiment of the present invention.
[0049] FIG. 23B is a view illustrating variations of a gray scale
voltage a liquid crystal display device according to a fifth
embodiment of the present invention.
[0050] FIG. 24A is a view illustrating variations of a gray scale
value in the liquid crystal display device.
[0051] FIG. 24B is a view illustrating variations of a gray scale
voltage in the liquid crystal display device.
[0052] FIG. 25A is a view illustrating variations of a gray scale
value in the liquid crystal display device.
[0053] FIG. 25B is a view illustrating variations of a gray scale
voltage in the liquid crystal display device.
[0054] FIG. 26 is a view illustrating an example of voltage
waveforms of scan lines in a liquid crystal display device
according to an application and modification of the present
invention.
[0055] FIG. 27 is a view illustrating an example of voltage
waveforms of scan lines in the liquid crystal display device.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0056] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings.
First Embodiment
[0057] First, a first embodiment as a basic aspect of the present
invention will be described. FIG. 1 is a schematic view
illustrating configuration of a liquid crystal display device 200
according to the first embodiment.
[0058] As shown in FIG. 1, the liquid crystal display device 200 as
an example of an electro-optical display device includes, as main
components, a data processing circuit 10, a timing control circuit
20, an X driver 30, Y drivers 40a and 40b, and a liquid crystal
display panel 50.
[0059] Of these components, the liquid crystal display panel 50
includes 480 rows of scan lines G.sub.1, G.sub.2, . . . ,
G.sub.240, G.sub.241, G.sub.242, . . . , G.sub.480 extending in a
horizontal direction and 640 columns of signal lines S.sub.1,
S.sub.2, S.sub.3, . . . , S.sub.640 extending in a vertical
direction. In addition, pixels 300 are arranged at intersections of
the 480 rows of scan lines and the 640 columns of 640 signal lines.
Accordingly, in this embodiment, the pixels are arranged in the
form of a 480 (in row).times.640 (in column) matrix. However, in
the invention, the pixels are not limited to this arrangement.
[0060] Now, configuration of the pixels 300 will be described with
reference to FIG. 2. FIG. 2A is a view illustrating an electrical
configuration of the pixels 300, showing four 2.times.2 pixels
arranged at intersections of an i-th row, an adjacent (i+1)-th row,
a j-th column and an adjacent (j+1)-th column. Here, i and (i+1),
which are integral numbers generally indicating rows at which the
pixels 300 are arranged, denote more than 1 but less than 480, and
j and (j+1), which are integral numbers generally indicating
columns at which the pixels 300 are arranged, denote more than 1
but less than 640.
[0061] As shown in FIG. 2A, each pixel 300 includes a liquid
crystal capacitor 320 and a thin film transistor (TFT) 316.
[0062] Here, since the pixels 300 have the same configuration, a
pixel located at an i-th row and a j-th column will be described
representatively. In the pixel located at the i-th row and the j-th
column, a gate of a TFT 316 is connected to a scan line G.sub.i at
the i-th row, a source thereof is connected to a signal line Sj at
the j-th column, and a drain thereof is a pixel electrode 318,
which is one end of the liquid crystal capacitor 320.
[0063] In addition, the other end of the liquid crystal capacitor
320 is connected to a common electrode 308. The common electrode
308 is common throughout the entire pixel 300. In this embodiment,
the common electrode 308 maintains a predetermined voltage LCcom in
a time manner.
[0064] As well known in the related art, the liquid crystal display
panel 50 is formed of a pair of substrates, i.e., an element
substrate and a counter substrate, with a predetermined gap
therebetween. In addition, the element substrate has an electrode
forming surface on which the scan lines, the signal lines, the TFT
316, and the pixel electrode 318 are formed. This electrode forming
surface is bonded to be opposite to the common electrode 308 formed
on the counter substrate. In addition, liquid crystal 305 is
interposed between the pixel electrode 318 and the common electrode
308. Accordingly, each pixel includes the liquid crystal capacitor
320, which is composed of the pixel electrode 318, the common
electrode 308 and the liquid crystal 305.
[0065] On opposite surfaces of both the substrates are individually
formed alignment films which are subject to a rubbing treatment
such that longitudinal axes of liquid crystal molecules are
consecutively twisted by about 90 degrees, for example. On the
other hand, on back sides of both the substrates are respectively
formed polarizers with their polarization axes aligned in an
orientation direction.
[0066] Accordingly, if an effective value of voltage applied to the
liquid crystal capacitor 320 is 0 V, since light passing between
the pixel electrode 318 and the common electrode 308 is rotated by
about 90 degrees due to the twisting of the liquid crystal
molecules, transmittance ratio of the light becomes maximal. On the
other hand, as the effective voltage increases, the liquid crystal
molecules are tilted in the direction of an electric field, and
accordingly, optical rotatory power is vanished. As a result, the
amount of transmission light is reduced and transmittance ratio is
minimized (normally white mode).
[0067] Accordingly, by applying a select voltage to the scan lines
to turn on the TFT 316 while applying a voltage depending on gray
scale, which is high (positive) or low (negative) with respect to
the voltage LCcom of the common electrode 308, to the pixel
electrode 318 by the signal lines and the turned-on TFT 316, it is
possible to maintain the effective voltage depending on the gray
scale predetermined at the liquid crystal capacitor 320.
[0068] In addition, while the TFT 316 is turned off when a
non-select voltage is applied to the scan lines, considerable
charges are leaked out of the liquid crystal capacitor 309 since an
off resistance of the turned-off TFT 316 does not become infinity,
ideally. A storage capacitor 309 is formed for each pixel in order
to lessen an effect of this off-leak. The storage capacitor 309 has
one end connected to the pixel electrode (the drain of TFT 316) and
the other end is commonly grounded to the entire pixels. The
storage capacitor 309 is provided in parallel to the liquid crystal
capacitor 320, while a voltage across the storage capacitor 309 is
maintained at a power voltage Vss (0 volt), for example, with
time.
[0069] Returning to FIG. 1, the data processing circuit 10 acquires
image data Da from an external super ordinate device. The image
data Da, which is data defining gray scale levels of the
480.times.640 pixels, is sequentially supplied in synchronization
with a synchronization signal Sync and a clock signal Clk. In this
embodiment, according to the image data Da, the gray scale levels
of the pixels are defined by 16 steps from a gray scale value 0
[0070] indicating the darkest state to a gray scale value 15
indicating the brightest state, for example. In addition, in this
embodiment, the image data Da includes a signal specifying whether
each pixel is marked with positive polarity or negative polarity.
Here, in this embodiment, considering the same pixel, a positive
mark and a negative mark are alternately reversed for each of the
plurality of frames. The reason for alternately reversing the mark
polarity between the positive and negative polarities is to prevent
the liquid crystal 305 from being deteriorated due to direct
application of current components.
[0071] The data processing circuit 10 performs a process, as will
be described below, for the acquired image data Da, and outputs
(processed) image data Db by defining a voltage to be applied to
the pixel electrode, that is, a voltage having a specified polarity
and depending on gray scale, for each pixel. In addition, in this
embodiment, as will be described below, one frame is divided into
two fields and the image data Db defines a voltage for each of the
two fields for each pixel.
[0072] The timing control circuit 20 generates a control signal
CtrX for controlling a horizontal scan by the X driver 30, control
signals CtrY1 and CtrY2 for controlling a vertical scan by the Y
drivers 40a and 40b, and a control signal CtrD for controlling a
processing timing in the data processing circuit 10 from the
synchronization signal Sync and the clock signal Clk supplied from
an external supply device.
[0073] The Y driver 40a is designed to scan the scan lines G1, G2,
. . . , G240 in the upper half of the 480 row scan lines based on
the control signal CtrY1 and the Y driver 40b is designed to scan
the scan lines G.sub.241, G.sub.242, . . . , G.sub.480 in the lower
half of the 480 row scan lines based on the control signal
CtrY2.
[0074] In the first embodiment, one frame is equally divided into
two fields when driving the liquid crystal display panel 50. Here,
one frame refers to an interval required to display one image
defined by the image data Da and is typically about 17 msec (the
reciprocal of a frequency 60 Hz). In addition, to distinguish
between the two fields constituting one frame, the previous one is
referred to as a first field and the later one is referred to as a
second field.
[0075] In such driving, the Y drivers 40a and 40b scan the 480 row
scan lines in one frame sequentially, as shown in FIG. 3, for
example.
[0076] That is, the scan lines G1, G2, . . . , G240 are scanned
sequentially in the first half of the first field and the scan
lines G.sub.241, G.sub.242, . . . , G.sub.480 are scanned
sequentially in the second half of the first field. This
configuration is the same as at the second field. Accordingly, in
each of the first and second fields, a scan line is exclusively
selected row-by-row sequentially from the top, and at the same
time, a high (H) level signal is supplied to the selected scan
line. As such, in this embodiment, a voltage is marked twice per
frame in each pixel 300.
[0077] The X driver 30 is designed to latch beforehand the image
data Db equivalent to one row of pixels located at the selected
scan line, based on the control signal Ctrx, and at the same time,
convert the latched image data Db to an analog voltage defined in
the image data Db and supply the analog voltage to the signal lines
S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.640 according to the
selection of the scan lines.
[0078] Now, the concept of a gray scale voltage, which is a voltage
applied to the pixel electrode 318, according to a gray scale value
and a mark polarity, will be described in reference to FIG. 6.
[0079] As described above, since this embodiment employs the
normally white mode, if the gray scale voltage has the positive
polarity, it becomes a high potential with respect to the voltage
LCcom of the common electrode 308 as the gray scale value becomes
small (that is, as a dark mode is designated). On the other hand,
if the gray scale voltage has the negative polarity, it becomes a
low potential with respect to the voltage LCcom as the gray scale
value becomes small.
[0080] In other words, when the gray scale voltage is applied to
the pixel electrode 318, the pixel has brightness corresponding to
the gray scale value designated in the image data Da.
[0081] A voltage having the positive polarity corresponding to each
gray scale value and a voltage having the negative polarity
corresponding to each gray scale value have a symmetrical
relationship with respect to the voltage LCcom. In addition, the
voltage Vss is a ground potential at a low value of a power
voltage, as described above. That is, the voltage Vss actually
becomes 0 V. In this embodiment, this ground potential is assumed
as the reference of a voltage without further explanation.
[0082] In addition, a magnitude relation of gray scale voltages for
two gray scale values is reversed if their mark polarities are
reversed. For example, a gray scale voltage corresponding to a gray
scale value of 1 is higher than a gray scale voltage corresponding
to a gray scale value of 3 if the mark polarity is positive, and,
on the contrary, the former is lower than the later if the mark
polarity is negative.
[0083] Here, in this embodiment, voltages actually outputtable by
the X driver 30 are just positive and negative voltages
corresponding to gray scale values of 0, 1, 3, 5, 7, 9, 11, 13 and
15 indicated by thick lines in FIG. 6. In this embodiment, gray
scale values other than these gray scale values indicated by the
thick lines are pseudo gray scale values using two different gray
scale levels (voltages) in the first and second fields.
[0084] In addition, while a voltage as a reference of the positive
and negative polarities is the voltage LCcom in this embodiment, in
some cases, this reference may be slightly displaced from the
voltage LCcom in order to prevent effective voltages from becoming
different from one another depending on their polarities due to
pushdown of TFTs.
[0085] Next, the data processing circuit 10 will be described in
detail. FIG. 4 is a block view illustrating a detailed
configuration of the data processing circuit 10.
[0086] In this figure, a frame memory 11 is designed to
sequentially store the image data Da supplied from the external
super ordinate device, read the stored image data Da after one
frame has lapsed, and output the read image data Da as image data
Dd. That is, the frame memory 11 delays the image data Da by only
one frame and outputs the image data Dd before the image data Da by
one frame.
[0087] A voltage determining unit 18 acquires the image data Da
supplied directly from the external super ordinate device and the
image data Dd read from the frame memory 11 and processes the
acquired image data Da and Dd, as will be described below, in order
to determine voltages for representing gray scale levels of the
pixels and output the image data Db for specifying the
voltages.
[0088] Here, while the image data Da from the external super
ordinate device is supplied in a dot-sequence manner over one frame
of the 480.times.640 pixels, the one frame is divided into the
first and second fields in this embodiment, as described above. To
this end, the voltage determining unit 18 processes the image data
Da corresponding to any pixel, and, when the image data Db is
output, outputs the image data Db specifying a voltage in the first
field if the first field is scanned in the liquid crystal display
panel 50 and outputs the image data Db specifying a voltage in the
second field if the second field is scanned.
[0089] That is, of the image data Db, a voltage for the first field
is equivalent to a first effective voltage and a voltage for the
second field is equivalent to a second effective voltage.
[0090] Next, a voltage determining process in the voltage
determining unit 18 will be described. FIG. 5 is a flow chart
illustrating contents of a voltage determining process. Even though
the voltage determining process is described here as the image data
Da of a pixel at an i-th row and a j-th column as a representative,
this process is actually performed in the dot-sequence manner for
all 480.times.640 pixels.
[0091] First, when the image data Da corresponding to the pixel at
the i-th row and j-th column are input from the external super
ordinate device (Step Sp1), the voltage determining unit 18 obtains
the image data Dd corresponding to the pixel at the same i-th row
and j-th column from the frame memory 11, that is, the image data
Dd before the image data Dd by one frame (Step Sp2). Also, since
the image data Da input from the external super ordinate device in
the current frame is stored in the frame memory 11, the image data
Da needs to be used for the next frame.
[0092] Next, the voltage determining unit 18 determines whether the
image data Da supplied from the external super ordinate device
corresponds to a first case of specifying one of the gray scale
values of 2, 4, 6, 8, 10, 12 and 14 (that is, in a case of
representing the pseudo gray scale values) or a second case of
specifying one of the gray scale values of 0, 1, 3, 5, 7, 9, 11, 13
and 15 (that is, in a case of not representing the pseudo gray
scale values) (Step Sp3).
[0093] In the first case, the voltage determining unit 18
additionally determines whether or not a gray scale voltage
specified in the image data Da supplied directly from the external
super ordinate device is varied from a gray scale voltage specified
in the image data Dd before the image data Da by one frame (Step
Sp4). As described above, the gray scale voltage refers to voltages
at an upper side according to the gray scale values with respect to
the voltage LCcom if a positive mark is designated, and refers to
voltages at a lower side according to the gray scale values with
respect to the voltage LCcom if a negative mark is designated (see
FIG. 6).
[0094] Accordingly, assuming that an output voltage of the x driver
30 has no restriction, it is determined in Step Sp4 whether or not
a voltage to be applied to a pixel electrode at the i-th row and
j-th column is varied over a range from a frame of the image data
Dd supplied from the frame memory (that is, the previous frame) to
a frame of the image data Da supplied from the external super
ordinate device (that is, the current frame).
[0095] In addition, if the gray scale voltages are varied, the
voltage determining unit 18 determines whether or not a polarity
reversion occurs (Step Sp5). Such determination is made because the
gray scale voltages are varied if the polarity reversion occurs
even if the gray scale values are not varied over the range from
the previous frame to the current frame.
[0096] If there is no variation in the polarity, the voltage
determining unit 18 determines whether or not the direction of
variation of the gray scale values is a direction at which it gets
dark (that is, a direction at which the gray scale values are
lowered) (Step Sp6).
[0097] Here, a gray scale value specified in the image data Da is
assumed as N. At this time, if the gray scale value is in the
direction at which it gets dark, the voltage determining unit 18
outputs the image data Db, with a gray scale value in the first
field as (N-1) and a gray scale value in the second field as (N+1),
for the pixel at the i-th row and j-th column (Step Sp7). In
addition, even if there is no variation in the gray scale values,
the gray scale voltages are varied when the polarity is reversed.
On this account, if a result of the determination in Step Sp5 is
NO, the process proceeds to Step Sp7 where the voltage determining
unit 18 outputs the same image data Db.
[0098] On the other hand, if the gray scale value is in the
direction at which it gets bright, the voltage determining unit 18
outputs the image data Db, with a gray scale value in the first
field as (N+1) and a gray scale value in the second field as (N-1),
for the pixel at the i-th row and j-th column (Step Sp8).
[0099] On the other hand, if it is determined in Step Sp3 that the
image data Da correspond to the second case, when the gray scale
value specified in the image data Da is assumed as N, the voltage
determining unit 18 outputs the image data Db, with gray scale
values in the first and second fields as N, for the pixel at the
i-th and j-th column (Step Sp9).
[0100] In addition, if it is determined in Step Sp4 that there is
no variation in the gray scale voltages, the voltage determining
unit 18 outputs the same image data Db as the previous frame for
the pixel at the i-th row and j-th column (Step Sp10).
[0101] In addition, in Steps Sp7 and Sp8 (Sp10 as circumstance
require), the gray scale values specified in the image data Db are
modified from the gray scale values specified in the image data Da,
however, the mark polarities are output as they are, with no
modification.
[0102] When one of Steps Sp7 to Sp10 is completed, the process for
the pixel at the i-th and j-th column is ended, and then, when
image data Da corresponding to a pixel at a next i-th and (j+1)-th
column is input, the above-described process is repeated.
[0103] On the other hand, in the first field of the current frame,
the scan lines G.sub.1, G.sub.2, G.sub.3, . . . , G.sub.480 become
an H level by the Y drivers 40a and 40b in the order shown in FIG.
3. Before the scan line G.sub.1 in the first field becomes an H
level, the X driver 30 is supplied with image data Db, which
correspond to the first field, of the image data Db at a first row
and first column, a first row and second column, a first row and
third column, . . . , a first and 640-th column. Then, in time when
the scan line G.sub.1 becomes the H level, the X driver 30 converts
the image data Db at the first row and first column, the first row
and second column, the first row and third column, . . . , the
first and 640-th column to an analog voltage specified in the mark
polarity and supplies the converted image data to the signal lines
S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.640.
[0104] When the scan line G.sub.1 is at H level, since the TFTs 316
in the pixels 300 at the first row are turned on, for example in
the first column, a voltage supplied to the signal line S.sub.1 is
applied to the pixel electrode 318 at the first row and first
column and accordingly, a voltage of an aimed gray scale value is
marked for the liquid crystal capacitor 320. This is true of pixels
at the second to 640-th columns.
[0105] Next, a scan line G.sub.2 becomes an H level. At this time,
similar to when the scan line G.sub.1 becomes the H level, a
voltage of a gray scale value specified in the image data Db at a
second row and first column, a second row and second column, a
second row and third column, . . . , a second and 640-th column is
marked for the liquid crystal capacitor 320. Likewise, scan line
G.sub.3, G.sub.4, . . . , G.sub.480 become an H level in order, and
voltages according to gray scale values specified in the image data
Db are marked for the liquid crystal capacitor 320.
[0106] Accordingly, each pixel maintains gray scale determined in
the voltage determining unit 18 over an interval up to a next mark,
that is, an interval (field) equivalent to half of one frame.
[0107] In the second field subsequent to the first field, like the
first field, the scan line G.sub.1, G.sub.2, G.sub.3, . . . ,
G.sub.480 become the H level and voltages according to gray scale
values of the image data Db are marked for each pixel. However, it
does not mean that the second field has the same gray scale values
as the first field for each pixel (Step Sp7 or Sp8). When the first
field has gray scale values different from those of the second, an
average gray scale of both fields will be perceived by a user when
viewed through one frame.
[0108] Next, in the first embodiment, marks obtainable when gray
scale values or mark polarities of the pixels are varied from an
immediate previous frame will be considered.
[0109] FIGS. 7A and 7B are views illustrating an example of
variation of gray scale voltages according to the gray scale values
specified in the image data Da and the mark polarities. In these
figures, a horizontal axis denotes time and a vertical axis denotes
a gray scale voltage.
[0110] In these figures, since only the variation of the gray scale
values specified in the image data Da is considered, there is no
need to consider whether or not the gray scale voltages are
voltages outputtable from the x driver 30. However, if the gray
scale voltages specified in the image data Db are considered, the
gray scale voltages are limited to voltages outputtable from the X
driver 30, that is, voltages corresponding to the gray scale value
of 0 and odd gray scale values.
[0111] FIG. 7A shows a state where the gray scale voltages
specified in the image data Da increase over a range from an (X-1)
frame to an X frame and are not varied over a range from an X frame
to an (X+1) frame. Here, since the image data Da specifies the gray
scale values and mark polarity of the pixels, as cases where the
gray scale voltages increase over the range from the (X-1) frame to
the X frame, three cases may be considered as follows:
[0112] (1) a case where the mark polarity is varied from a positive
polarity to a negative polarity,
[0113] (2) a case where the mark polarity is not varied from the
positive polarity but the gray scale values decrease (i.e., are
varied in a direction in which it becomes dark),
[0114] (3) a case where the mark polarity is not varied from the
negative polarity but the gray scale values increase (i.e., are
varied in a direction in which it becomes bright).
[0115] Next, FIG. 7B shows a state where the gray scale voltages
decrease over the range from the (X-1) frame to the X frame and are
not varied over the range from the X frame to the (X+1) frame. As
cases where the gray scale voltages decrease over the range from
the (X-1) frame to the X frame, three cases may be considered as
follows:
[0116] (4) a case where the mark polarity is varied from the
positive polarity to the negative polarity,
[0117] (5) a case where the mark polarity is not varied from the
negative polarity but the gray scale values decrease (i.e., are
varied in a direction in which it becomes dark),
[0118] (6) a case where the mark polarity is not varied from the
positive polarity but the gray scale values increase (i.e., are
varied in a direction in which it becomes bright).
[0119] In the end, the variation of the gray scale voltages are
varied may be classified into the above six cases (1) to (6).
[0120] The above cases (1) to (4) are independent of whether or not
the gray scale values are predetermined. This embodiment is carried
out in the normally white mode, as described above.
[0121] Next, assuming that the X frame is the current frame, if the
gray scale values specified in the image data Da are an even number
except 0, a result of the determination in Step Sp3 is `YES`. Here,
since the variation of the gray scale voltages is considered, a
result of the determination in Step Sp4 is also `YES`.
[0122] Subsequently, a case where a result of the determination in
Step Sp5 is `NO` corresponds to cases (1) and (4), and a case where
a result of the determination in Step Sp5 is `YES` corresponds to
cases (2), (3), (5) and (6). Of these cases, a case where a result
of the determination in Step Sp6 is `YES` corresponds to cases (2)
and (5).
[0123] In the end, in cases (1), (2), (4) and (5), through Step
Sp7, the gray scale value of the image data Db becomes a gray scale
value (N-1), which is smaller by 1 than the gray scale value N
specified in the image data Da, for the first field, and becomes a
gray scale value (N+1), which is larger by 1 than the gray scale
value N, for the second field. Here, since the gray scale value N
specified in the image data Da is an even gray scale value except
0, it is not a voltage outputtable from the X driver 30. However,
since the gray scale values smaller and larger by 1 than the gray
scale value N are an odd gray scale value, they are voltages
outputtable from the x driver 30.
[0124] In cases (1) and (2), since the mark polarity is positive,
the gray scale voltages specified in the image data Db in the X
frame are as shown in FIG. 8A. More specifically, the gray scale
voltages specified in the image data Db of the X frame become a
voltage corresponding to the gray scale value (N-1) shifted in an
increasing direction as a variation direction, rather than a
voltage corresponding to the gray scale value N, for the first
field, and become a voltage corresponding to the gray scale value
(N+1) shifted in a decreasing direction opposite to the variation
direction, rather than the voltage corresponding to the gray scale
value N, for the second field.
[0125] In addition, in cases (4) and (5), since the mark polarity
is negative, the gray scale voltages specified in the image data Db
in the X frame are as shown in FIG. 9B. More specifically, the gray
scale voltages specified in the image data Db of the X frame become
a voltage corresponding to the gray scale value (N-1) shifted in a
decreasing direction as a variation direction, rather than the
voltage corresponding to the gray scale value N, for the first
field, and become a voltage corresponding to the gray scale value
(N+1) shifted in an increasing direction opposite to the variation
direction, rather than the voltage corresponding to the gray scale
value N, for the second field.
[0126] On the other hand, a case where a result of the
determination in Step Sp6 is `NO` corresponds to cases (3) and
(6).
[0127] In cases (3) and (6), through Step Sp8, the gray scale value
of the image data Db becomes a gray scale value (N+1), which is
larger by 1 than the gray scale value N specified in the image data
Da, for the first field, and becomes a gray scale value (N-1),
which is smaller by 1 than the gray scale value N, for the second
field.
[0128] In case (3), since the mark polarity is negative, the gray
scale voltages specified in the image data Db in the X frame are as
shown in FIG. 8B. More specifically, the gray scale voltages
specified in the image data Db of the X frame become a voltage
corresponding to the gray scale value (N+1) shifted in an
increasing direction as a variation direction, rather than the
voltage corresponding to the gray scale value N, for the first
field, and become a voltage corresponding to the gray scale value
(N-1) shifted from the voltage corresponding to the gray scale
value (N+1) in a decreasing direction opposite to the variation
direction, rather than the voltage corresponding to the gray scale
value N, for the second field.
[0129] In addition, in case (6), since the mark polarity is
positive, the gray scale voltages specified in the image data Db in
the X frame are as shown in FIG. 9A. More specifically, the gray
scale voltages specified in the image data Db of the x frame become
a voltage corresponding to the gray scale value (N+1) shifted in a
decreasing direction as a variation direction, rather than the
voltage corresponding to the gray scale value N, for the first
field, and become a voltage corresponding to the gray scale value
(N-1) shifted in an increasing direction opposite to the variation
direction, rather than the voltage corresponding to the gray scale
value N, for the second field.
[0130] However, when the gray scale value specified in the image
data Da in the X frame is an odd number, since the gray scale value
is a voltage outputtable from the X driver 30, in this embodiment,
the gray scale value of the image data Db is the gray scale value N
specified in the image data Da for the first and second fields
through Step Sp9, regardless of whether or not the gray scale
voltages are varied. On this account, when the gray scale value N
specified in the image data Da in the X frame is an odd number, the
gray scale voltage specified in the image data Db becomes a voltage
corresponding to the odd gray scale value N over the first and
second fields, as shown in FIG. 10A if the gray scale voltage is
positive and as shown in FIG. 10B if the gray scale voltage is
negative.
[0131] In a case where the gray scale value specified in the image
data Da is an even number except 0, when the gray scale voltage is
not varied (that is, when a result of the determination in Step
Sp4), in this embodiment, the image data Db in an immediate
previous frame is again output through Step Sp10. In FIGS. 8A, 8B,
9A, 9B, 10A and 10B, since the gray scale voltage is not varied
over the range from the X frame to the (X+1) frame, the gray scale
voltage specified in the image data Db of the (X+1) frame is the
same as the X frame for the first and second fields.
[0132] According to the first embodiment, when the gray scale value
or the mark polarity is varied, since an excess is offset with a
voltage marked to the liquid crystal capacitor as an excessive
voltage shifted in the variation direction, rather than a voltage
corresponding to the gray scale value specified in the image data
Da, in the first field and as a voltage shifted in a direction
opposite to the variation direction, rather than the voltage
corresponding to the gray scale value specified in the image data
Da, in the subsequent second field, it is possible to improve the
responsiveness of the liquid crystal 305 having a relatively slow
response speed. In addition, in this embodiment, even when gray
scale to be represented for one frame corresponds to a voltage
which can not be output from the X driver 30, since the gray scale
includes pseudo values represented in the first and second fields
using the gray scale values corresponding to the voltages
outputtable from the X driver 30, it is possible to increase the
number of representable gray scale levels.
[0133] In addition, in this embodiment, in only a case where the
gray scale value specified by the image data Da in a frame to be
processed is not a gray scale value corresponding to the
outputtable voltage of the X driver 30, the gray scale voltage of
the first field becomes different from the gray scale voltage of
the second field through Step Sp7 or Sp8. However, even though the
gray scale value specified by the image data Da is the gray scale
value corresponding to the outputtable voltage of the X driver 30,
when the gray scale voltage of the first field becomes different
from the gray scale voltage of the second field through Step Sp7 or
Sp8, improvement in the response speed can be expected. On this
account, regardless of whether or not the gray scale voltages
specified by the image data Da for the frame to be processed are
the outputtable voltage of the X driver 30, it may be configured
that the gray scale voltage shifted in the variation direction of
the gray scale voltage from the previous frame is applied to the
first frame and the gray scale voltage shifted in the opposite
direction to the variation direction is applied to the subsequent
field (this configuration will be described in detail in a fourth
embodiment, which will be described later).
[0134] Here, in a case where it is not determined in Step Sp3
whether or not the gray scale value specified by the image data Da
is the gray scale value corresponding to the outputtable voltage of
the X driver 30, if the gray scale value specified by the image
data Da of the frame to be processed is, for example, a gray scale
value of 0 or 15 (minimum or maximum value), the gray scale value
in the first field can not become different from the gray scale
value in the second field. Accordingly, instead, it is preferable
that it may be determined in Step Sp3 whether or not the gray scale
value specified by the image data Da is the gray scale value
corresponding to the outputtable voltage of the x driver 30.
[0135] In addition, in the first embodiment, if there is no
variation in the gray scale voltages (that is, if a result of the
determination in Step Sp4 is NO), it is configured that the image
data Db having the same contents as the previous frame are again
output through Step Sp10. However, as shown in FIG. 11, it may be
configured that the gray scale voltages of the first and second
fields in the previous frame (here, the X frame) are altered and a
frame having the altered gray scale voltages is output as the
current frame (here, (X+1) frame).
[0136] With such a configuration, since a variation period of the
gray scale voltage applied to the pixel electrodes is reduced by
half and the amount of charge and discharge per unit time in the
liquid crystal capacitor 320 decreases, it is possible to suppress
power consumption.
[0137] In the first embodiment, in a case where the gray scale
value N specified by the image data Da in the frame to be processed
is not the gray scale value corresponding to the outputtable
voltage of the X driver 30, if the gray scale voltage is varied,
two gray scale values specified in the image data Db are (N+1) and
(N-1) independent of the amount of variation of the gray scale
voltage. However, if the amount of variation is large, a difference
between the two gray scale values may become large depending on the
amount of variation. For example, for the gray scale value N
specified by the image data Da in the frame to be processed, if the
amount of variation of the gray scale voltage from the immediate
previous frame is large, two gray scale values specified in the
image data Db may be assumed as (N+3) and (N-3).
[0138] In addition, in a case where a difference between two gray
scale values specified in the image data Db are varied depending on
the amount of variation, there may be no difference between the two
gray scale values depending on the gray scale values specified in
the image data Da. For example, if the gray scale value specified
by the image data Da of the frame to be processed is, for example,
the gray scale value of 0 or 15 (minimum or maximum value), the
gray scale value can not be (N+3) or (N-3). On this account, it may
be determined whether or not the gray scale values specified by the
image data Da correspond to the a minimum or maximum gray scale
value.
[0139] In addition, in the first embodiment, it is determined in
Step Sp4 whether or not the gray scale voltages are varied.
However, even if there is any variation of gray scale voltages,
such variation may be disregarded in some cases, for example, in a
case where the gray scale values are minutely varied since mark
polarities are identical to each other. On this account, when it is
determined that the gray scale voltages are varied, if the amount
of variation of the gray scale voltages exceeds a predetermined
threshold, the process may proceed to Step Sp5.
[0140] In addition, in the first embodiment, the Y drivers 40a and
40b scan the scan lines in the order as shown in FIG. 3. However,
as shown in FIG. 12, the Y drivers 40a and 40b may alternately scan
the scan lines in the order of from the top to the bottom. That is,
the scan lines may be scanned in the order of G.sub.1, G.sub.241,
G.sub.2, G.sub.242, G.sub.3, G.sub.243, . . . , G.sub.240,
G.sub.480 for the first field, and may be scanned in the same order
for the second field.
[0141] In such a scan, when scan lines are selected on every other
scan line, like the scan lines G.sub.1, G.sub.2, G.sub.3, . . . ,
G.sub.240 in the first field and the scan lines G.sub.241,
G.sub.242, G.sub.243, . . . , G.sub.480, since that order becomes
the scan lines G.sub.1.fwdarw.G.sub.480 for one frame, each of the
Y drivers 40a and 40b may drive the scan lines at a conventional
speed (a speed at which the scan lines G.sub.1 to G.sub.480 are
scanned once during one frame).
Second Embodiment
[0142] In the above-described first embodiment, the voltage
determining unit 18 obtains the image data Db for each pixel
according to the process shown in FIG. 5 using the image data Da of
the current frame and the image data Dd of the previous frame. That
is, in the first embodiment, the image data Db is obtained from the
image data Da and the image data Dd through a specific
calculation.
[0143] However, the invention is not limited to the first
embodiment. For example, it may be configured that a plurality of
voltage patterns are set in advance, one voltage pattern is
selected from the image data Da and the image data Dd, and the
selected voltage pattern is output as the image data Db.
[0144] From the point of view of such a configuration, a second
embodiment is to construct the voltage determining unit 18.
[0145] A liquid crystal display device according to the second
embodiment is generally similar to that according to the first
embodiment shown in FIG. 1, but is different in a detailed
configuration of the data processing circuit 10 including the
voltage determining unit 18 from the first embodiment. Therefore,
the second embodiment will be described focusing on the difference
in the data processing circuit 10.
[0146] FIG. 13 is a block diagram illustrating configuration of the
data processing circuit 10 according to the second embodiment.
[0147] As shown in the figure, the data processing circuit 10 is
similar to that shown in FIG. 4 in that it includes the frame
memory 11 and the voltage determining unit 18. However, the voltage
determining unit 18 of the second embodiment further includes a
decoder 12, a calculating unit 13, a voltage pattern storing unit
14, a voltage pattern selecting unit 15, and a discriminating unit
16.
[0148] Of these components, the decoder 12 decodes the gray scale
values specified in the image data Da of the current frame and the
mark polarity and acquires the gray scale voltages specified in the
image data Da.
[0149] On the other hand, the calculating unit 13 subtracts the
gray scale voltages specified in the image data Dd of the previous
frame from the gray scale voltages specified in the image data Da
of the current frame, that is, a difference between the gray scale
voltages over the range from the previous frame to the current
frame, for the same pixel, and outputs a signal 152 representing
the obtained difference.
[0150] The voltage pattern storing unit 14 stores three kinds of
voltage patterns specifying the gray scale voltages in the first
and second fields, more specifically, a first pattern 14a, a second
pattern 14b and a third pattern 14c, as shown in FIG. 14.
[0151] Of these patterns, the first pattern 14a is a voltage
pattern where the gray scale voltages specified in the image data
Da are specified, as they are, for the first and second fields.
That is, the first pattern 14a is a voltage pattern as specified in
Step Sp9 in the first embodiment.
[0152] Next, the second pattern 14b is a voltage pattern where the
gray scale voltages used in the first field are higher than the
gray scale voltages specified in the image data Da and the gray
scale voltages used in the second field are lower than the gray
scale voltages specified in the image data Da. That is, the second
pattern 14b is a voltage pattern as specified in Step Sp7 when the
positive mark is specified (see FIG. 8A) and in Step Sp8 when the
negative mark is specified (see FIG. 8B) in the first
embodiment.
[0153] In addition, the third pattern 14c is a voltage pattern
where the gray scale voltages used in the first field are lower
than the gray scale voltages specified in the image data Da and the
gray scale voltages used in the second field are higher than the
gray scale voltages specified in the image data Da. That is, the
third pattern 14c is a voltage pattern as specified in Step Sp8
when the positive mark is specified (see FIG. 9A) and in Step Sp7
when the negative mark is specified (see FIG. 9B) in the first
embodiment.
[0154] In addition, the voltage pattern storing unit 14 sets an
average value of the gray scale voltages of the first and second
fields to be gray scale voltages decoded in the decoder 12, that
is, the gray scale voltages specified in the image data Da, in the
first pattern 14a, the second pattern 14b and the third pattern
14c. Accordingly, an average value of the gray scale voltages at
any voltage pattern is equal to the gray scale voltages specified
in the image data Da.
[0155] The discriminating unit 16 discriminates whether or not the
difference between the gray scale voltages is 0 based on the signal
152. In addition, as described in the above first embodiment, even
if there is any variation of gray scale voltages, there is a case
where such variation may be disregarded. In this case, the
discriminating unit 16 discriminates whether or not the difference
between the gray scale voltages exceeds a predetermined
threshold.
[0156] The voltage pattern selecting unit 15 selects one voltage
pattern stored in the voltage pattern storing unit 14 based on the
signal supplied from the calculating unit 13 and a result of the
discrimination in the discriminating unit 16, and outputs the image
data Db specified in the selected voltage pattern to the first and
second fields.
[0157] More specifically, the voltage pattern selecting unit 15
selects the first pattern 14a when the gray scale voltages
specified in the image data Da (the gray scale voltages decoded in
the decoder 12) is the outputtable voltage of the X driver 30, and
selects a voltage pattern as follows when the gray scale voltages
specified in the image data Da is not the outputtable voltage of
the X driver 30. That is, when the gray scale voltages specified in
the image data Da is not the outputtable voltage of the X driver
30, the voltage pattern selecting unit 15 selects the second
pattern 14b if it is discriminated in the discriminating unit 16
that the difference between the gray scale voltages is not 0 but
positive (that is, the variation direction is the increasing
direction), and selects the third pattern 14c if it is determined
that the difference is negative (that is, the variation direction
is the decreasing direction).
[0158] In addition, when the gray scale voltages decoded in the
decoder 12 is not the outputtable voltage of the X driver 30, the
voltage pattern selecting unit 15 again outputs a voltage pattern
selected in the previous frame also in the current frame if it is
discriminated in the discriminating unit 16 in which the difference
between the gray scale voltages is 0. A voltage pattern determining
unit is constituted by the voltage pattern storing unit 14 and the
voltage pattern selecting unit 15.
[0159] Here, a voltage pattern selected in the voltage pattern
selecting unit 15 will be considered.
[0160] A point that the first pattern 14a is selected when the gray
scale voltages decoded in the decoder 12 is the outputtable voltage
of the X driver 30 corresponds to the point that, in the first
embodiment, the result of the determination in Step Sp3 is `NO`,
and the gray scale values of the first and second fields for the
image data Db are assumed as the gray scale value N specified in
the image data Da in Step Sp9.
[0161] Next, a case where the difference between the gray scale
voltages over the range from the previous frame to the current
frame is positive when the gray scale voltages decoded in the
decoder 12 is not the outputtable voltage of the X driver 30
corresponds to cases (1), (2) and (3) in the first embodiment.
[0162] In addition, a case where the difference between the gray
scale voltages over the range from the previous frame to the
current frame is negative when the gray scale voltages decoded in
the decoder 12 is not the outputtable voltage of the X driver 30
corresponds to cases (4), (5) and (6) in the first embodiment.
[0163] In addition, a case where the difference between the gray
scale voltages over the range from the previous frame to the
current frame is 0 when the gray scale voltages decoded in the
decoder 12 is not the outputtable voltage of the X driver 30
corresponds to the point that, in the first embodiment, the result
of the determination in Step Sp3 is `YES`, the result of the
determination in Step Sp4 is `NO`, and the same image data Db as
the previous frame are output again in Step Sp10.
[0164] On this account, when the voltage pattern is selected in the
voltage pattern selecting unit 15 in the second embodiment, the
image data Db specified in the selected voltage pattern are exactly
the same as the first embodiment. Accordingly, also in the second
embodiment, it is possible to improve the responsiveness of the
liquid crystal and increasing the number of representable gray
scale levels.
Third Embodiment
[0165] In the first and second embodiments, it is configured that
one frame is divided into the first and second fields and the mark
of voltages to the pixels is performed twice per one frame,
however, the present invention is not limited to this
configuration. Now, a third embodiment in which one frame is
divided into four fields will be described.
[0166] A liquid crystal display device according to the third
embodiment is generally similar to that according to the first
embodiment shown in FIG. 1, except that one frame is divided into
four fields. For the sake of convenience, the four fields are
referred to as first, second, third, and fourth fields in order
from the earliest to the lasts in time.
[0167] The timing control circuit 20 controls the Y drivers 40a and
40b to scan the scan lines in the order as shown in FIG. 15, for
example. As a result, the scan lines G1, G2, . . . , G240 are
scanned sequentially in the first half of the first field and the
scan lines G.sub.241, G.sub.242, . . . , G.sub.480 are scanned
sequentially in the second half of the first field. The scan is
also the same as the subsequent second, third and fourth fields.
Accordingly, as a result, the scan lines are exclusively selected
row-by-row in order from the top, and an H level signal is supplied
to the selected scan lines. On this account, in this embodiment, a
mark is performed four times for one frame in each pixel 300.
[0168] In addition, the third embodiment is similar to the first
embodiment in that the X driver 30 converts the image data Db
corresponding to one row of pixels located on the selected scan
lines to an analog signal and supplies the analog signal to the
signal line S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.640.
[0169] In addition, the liquid crystal display device according to
the third embodiment is different from the first and second
embodiments in a relationship between the gray scale values
corresponding to the voltages outputtable from the X driver 30 and
the gray scale values represented pseudo gray scale values using
the gray scale value corresponding to the voltages outputtable from
the X driver 30.
[0170] Here, this relationship will be described with reference to
FIG. 16. In FIG. 16, a horizontal axis denotes gray scale.
[0171] In this drawing, p1, r1, r2, r3 and p2 are adjacent gray
scale values specified in the image data Da arranged at an equal
interval. Of these gray scale values, the gray scale values p1 and
p2 are gray scale values corresponding to the outputtable voltages
of the X driver 30, but the gray scale values r1, r2, and r3 do not
correspond to the outputtable voltages of the X driver 30.
[0172] In addition, here, only the gray scale values p1 and p2 of
the gray scale values corresponding to the outputtable voltage of
the X driver 30 are extracted.
[0173] On the other hand, the voltage determining unit 18 according
to the third embodiment assumes the same configuration as the
second embodiment, however, it is different from the third
embodiment by a voltage pattern stored in the voltage pattern
storing unit 14. Now, this voltage pattern will be described with
reference to FIGS. 17A, 17B and 17C. In these drawings, a
horizontal axis denotes time (field) and a vertical axis denotes a
gray scale voltage.
[0174] Here, FIG. 17A shows a first pattern (group), FIG. 17B shows
a second pattern, and FIG. 17C shows a third pattern. These voltage
patterns are stored in advance in the voltage pattern storing unit
14.
[0175] Here, the first pattern corresponds to a case where the gray
scale voltages are not varied over the range from the previous
frame to the current frame, and are divided into five voltage
patterns 71 to 75. These voltage patterns 71 to 75 correspond to
the gray scale values p1, r1, r2, r3, and p2, respectively.
[0176] The second pattern corresponds to a case where the gray
scale voltages increase over the range from the previous frame to
the current frame, and are divided into five voltage patterns 81 to
85. These voltage patterns 81 to 85 correspond to the gray scale
values p1, r1, r2, r3, and p2, respectively.
[0177] The third pattern corresponds to a case where the gray scale
voltages decrease over the range from the previous frame to the
current frame, and are divided into five voltage patterns 91 to 95.
These voltage patterns 91 to 95 correspond to the gray scale values
p1, r1, r2, r3, and p2, respectively.
[0178] In the third embodiment, if it is discriminated in the
discriminating unit 16 in which the difference between the gray
scale voltages over the range from the previous frame to the
current frame is 0, the voltage pattern selecting unit 15 in the
data processing circuit 10 selects a voltage, which corresponds to
the gray scale values specified in the image data Da, of the first
pattern. In addition, if it is discriminated in the discriminating
unit 16 that the difference between the gray scale voltages is not
0, the voltage pattern selecting unit 15 selects a voltage, which
corresponds to the gray scale values specified in the image data
Da, of the second pattern if the difference is positive (that is,
the variation direction is the increasing direction) and selects a
voltage, which corresponds to the gray scale values specified in
the image data Da, of the third pattern if the difference is
negative (that is, the variation direction is the decreasing
direction).
[0179] In FIGS. 17A, 17B and 17C, gray scale voltages P1 and P2 are
voltages corresponding to the gray scale values p1 and p2,
respectively, considering the mark polarity, with a relationship of
P1<P2.
[0180] Here, when a bright state is designated as the gray scale
values increase in the normally white mode, the gray scale voltage
relationship of P1<P2 is established when the gray scale values
p1>p2 if a positive mark is designated and when the gray scale
values p1<p2 if a negative mark is designated. In this manner,
since the magnitude relationship of the gray scale voltages P1 and
P2 for the two gray scale values p1 and p2 is reversed by the mark
polarity, the gray scale values shown in FIG. 16 have a
relationship of p1>r1>r2>r3>p2 when the positive mark
is designated and a relationship of p1<r1<r2<r3<p2 when
the negative mark is designated.
[0181] Also in consideration, the voltage patterns 71, 81 and 91
represent patterns of the gray scale voltages used when the gray
scale value p1 is represented. More specifically, if a gray scale
value specified in the image data Da is p1, the gray scale value p1
and the gray scale voltage P1 specified by the mark polarity are
predetermined through the first to fourth fields.
[0182] In addition, the voltage patterns 71, 81 and 91 are the
same. Accordingly, when any one of the first, second and third
patterns is selected in the voltage pattern selecting unit 15 (that
is, regardless of the variation of the gray scale voltages from the
previous frame when the gray scale values specified in the image
data Da of the current frame), the voltage patterns 71, the
selected pattern has apparently the same pattern 71 (81, 91).
[0183] Next, the voltage patterns 72, 82 and 92 represent patterns
of the gray scale voltages used when the gray scale value r1 is
represented.
[0184] The voltage pattern 72 belonging to the first pattern
becomes the gray scale voltage P1 corresponding to the gray scale
value p1 close to the gray scale value r1 in the first, third and
fourth fields and becomes the gray scale voltage P2 corresponding
to the gray scale value p2 distant from the gray scale value r1 in
the second field.
[0185] The voltage pattern 82 belonging to the second pattern
becomes the gray scale voltage P1 in the second, third and fourth
fields and becomes the gray scale voltage P2 in the first field. As
described above, since the second pattern is selected when the gray
scale voltages specified in the image data Da over the range from
the previous frame to the current frame increase, the gray scale
voltage P2 shifted in the increasing direction as the variation
direction is applied to the pixel electrode (in the first field)
prior to a voltage corresponding to the gray scale value r1, and
thereafter, the gray scale voltage P1 shifted in the decreasing
direction opposite to the variation direction is applied to the
pixel electrode (after the first second) prior to the voltage
corresponding to the gray scale value r1.
[0186] The voltage pattern 92 belonging to the third pattern
becomes the gray scale voltage P1 in the first, second and fourth
fields and becomes the gray scale voltage P2 in the third field. As
described above, since the third pattern is selected when the gray
scale voltages specified in the image data Da over the range from
the previous frame to the current frame decrease, the gray scale
voltage P1 shifted in the decreasing direction as a variation
direction is applied to the pixel electrode (in the first and
second fields) prior to the voltage corresponding to the gray scale
value r1, and thereafter, the gray scale voltage P2 shifted in the
increasing direction opposite to the variation direction is applied
to the pixel electrode (in the third field) prior to the voltage
corresponding to the gray scale value r1, and the gray scale
voltage P1 is again applied to the pixel electrode (in the fourth
field).
[0187] Subsequently, the voltage patterns 73, 83 and 93 represent
patterns of the gray scale voltages used when the gray scale value
r2 is represented.
[0188] The voltage pattern 73 belonging to the first pattern and
the voltage pattern 83 belonging to the second pattern becomes the
gray scale voltage P1 in the second and fourth fields and becomes
the gray scale voltage P2 in the first and third fields. Since the
voltage pattern 83 of these voltage patterns considers a case where
the gray scale voltages specified in the image data Da increase,
the gray scale voltage P2 shifted in the increasing direction as
the variation direction is applied to the pixel electrode (in the
first field) prior to a voltage corresponding to the gray scale
value r2, and thereafter, the gray scale voltage P1 shifted in the
decreasing direction opposite to the variation direction is applied
to the pixel electrode (in the second field).
[0189] The voltage pattern 93 belonging to the third pattern
becomes the gray scale voltage P1 in the first and third fields and
becomes the gray scale voltage P2 in the second and fourth fields.
Since the voltage pattern 93 considers a case where the gray scale
voltages specified in the image data Da decrease, the gray scale
voltage P1 shifted in the decreasing direction as the variation
direction is applied to the pixel electrode (in the first field)
prior to the voltage corresponding to the gray scale value r2, and
thereafter, the gray scale voltage P2 shifted in the increasing
direction opposite to the variation direction is applied to the
pixel electrode (in the second field).
[0190] The voltage patterns 74, 84 and 94 represent patterns of the
gray scale voltages used when the gray scale value r3 is
represented.
[0191] The voltage pattern 74 belonging to the first pattern and
the voltage pattern 84 belonging to the second pattern become the
gray scale voltage P2 corresponding to the gray scale value p2
close to the gray scale value r3 in the first, second and third
fields and become the gray scale voltage P1 corresponding to the
gray scale value p1 distant from the gray scale value r3 in the
fourth field. Since the voltage pattern 84 of these voltage
patterns considers a case where the gray scale voltages specified
in the image data Da increase, the gray scale voltage P2 shifted in
the increasing direction as the variation direction is applied to
the pixel electrode (in the first, second and third fields) prior
to a voltage corresponding to the gray scale value r3, and
thereafter, the gray scale voltage P1 shifted in the decreasing
direction opposite to the variation direction is applied to the
pixel electrode (in the second field) prior to the voltage
corresponding to the gray scale value r1.
[0192] The voltage pattern 94 belonging to the third pattern
becomes the gray scale voltage P1 in the first field and becomes
the gray scale voltage P2 in the second, third and fourth fields.
Since the voltage pattern 94 considers a case where the gray scale
voltages specified in the image data Da decrease, the gray scale
voltage P1 shifted in the decreasing direction as the variation
direction is applied to the pixel electrode (in the first field)
prior to the voltage corresponding to the gray scale value r3, and
thereafter, the gray scale voltage P2 shifted in the increasing
direction opposite to the variation direction is applied to the
pixel electrode (after the second field) prior to the voltage
corresponding to the gray scale value r3.
[0193] The voltage patterns 75, 85 and 95 represent patterns of the
gray scale voltages used when the gray scale value p2 is
represented. More specifically, if a gray scale value specified in
the image data Da is p2, the gray scale value p2 and the gray scale
voltage P2 specified by the mark polarity are predetermined through
the first to fourth fields.
[0194] Next, in the third embodiment, marks obtainable when the
gray scale values or mark polarities of the pixels are varied from
the immediate previous frame will be considered.
[0195] FIG. 18A is a view illustrating variation of the gray scale
values specified in the image data Da of one pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0196] As shown in this drawing, the image data Da is input in
order of an (X-1) frame, an X frame and an (X+1) frame. More
specifically, the gray scale value p1 is specified in the (X-1)
frame and the gray scale value r1 is specified in the X frame and
the (X+1) frame. Accordingly, the gray scale value is varied from
the gray scale value p1 to the gray scale value r1 over a range
from the (X-1) frame to the X frame. In addition, a negative
polarity is designated through the (X-1) frame, the X frame and the
(X+1) frame.
[0197] FIG. 18B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18), that is, a voltage applied to the
pixel electrode of a pixel to be considered, when the gray scale
values specified in the image data Da are varied as shown in FIG.
18A. In this drawing, a horizontal axis denotes time and a vertical
axis denotes a gray scale voltage.
[0198] By the way, when a gray scale value specified in the image
data Da in the (X-1) frame is p1, a gray scale voltage in the (X-1)
frame becomes P1 corresponding to the gray scale value p1,
regardless of variation of the gray scale voltages from the
previous (X-2) frame (not shown), as described above.
[0199] The gray scale value r1 specified in the image data Da in
the X frame does not correspond to the outputtable voltages of the
X driver 30. In addition, the gray scale value is varied from the
gray scale value p1 of the previous (X-1) frame to the gray scale
value r1. Here, since the negative polarity is designated, a
relationship of p1<r1 is established, and the gray scale
voltages specified in the image data Da increase over the range
from the (X-1) frame to the X frame and a difference between the
gray scale voltages is positive. On this account, the voltage
pattern selecting unit 15 selects the voltage pattern 82 belonging
to the second pattern and corresponding to the gray scale value r1.
Accordingly, the image data Db corresponding to the pixel become
the gray scale voltage P2 in the first field of the X frame and the
gray scale voltage P1 in the subsequent second, third and fourth
fields.
[0200] When the gray scale voltages are increased in the X frame,
since the gray scale voltage P2 shifted in the increasing direction
in the first field is marked to the liquid crystal capacitor of the
pixel prior to the voltage corresponding to the gray scale value p1
specified in the image data Da, it is possible to improve the
responsiveness of the liquid crystal 305 having a relatively low
response speed. In addition, the gray scale value r1 is located on
a point at which a distance between the gray scale value p1 and the
gray scale value p2 is divided internally with a ratio of 1:3, and
the gray scale voltage P1 corresponding to the gray scale value p1
is applied to the pixel electrode over the sum of three fields of
the second, third and fourth fields, while the gray scale voltage
P2 corresponding to the gray scale value p2 is applied to the pixel
electrode only during the first field. Accordingly, the gray scale
levels are almost represented as the pseudo values when one frame
is viewed.
[0201] Even though the gray scale value r1 specified in the image
data Da in the (X+1) frame does not correspond to the outputtable
voltages of the X driver 30, the gray scale value is not varied
from the gray scale value r1 of the previous X frame. On this
account, the voltage pattern selecting unit 15 selects the voltage
pattern 72 belonging to the first pattern and corresponding to the
gray scale value r1. Accordingly, the image data Db corresponding
to the pixel to be considered becomes the gray scale voltage P1 in
the first field of the (X+1) frame, the gray scale voltage P2 in
the subsequent second field, and again the gray scale voltage P1 in
the subsequent third and fourth fields.
[0202] When corresponding scan lines in each field of one frame are
selected, the image data Db corresponding to the field are
converted to an analog signal by the x driver 30 and the analog
signal is applied to corresponding signal lines. Accordingly, the
gray scale voltages specified in the image data Db are applied to
the pixel electrode.
[0203] The pseudo gray scale value of the gray scale value r1 in
the (X-1) frame is similar to the previous X frame.
[0204] In this example, the case where the gray scale voltages
specified in the image data Da increase has been described. Now, a
case where the gray scale voltages specified in the image data Da
decrease will be considered.
[0205] FIG. 19A is a view illustrating variation of the gray scale
values specified in the image data Da of one pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0206] As shown in this drawing, the gray scale value p2 is
specified in the (X-1) frame and the gray scale value r1 is
specified in the X frame and the (X+1) frame. Accordingly, the gray
scale value is varied from the gray scale value p2 to the gray
scale value r1 over the range from the (X-1) frame to the X frame.
In addition, a negative polarity is designated through the (X-1)
frame, the X frame and the (X+1) frame.
[0207] FIG. 19B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18) and applied to the pixel electrode of
the pixel to be considered, based on the above-mentioned condition
setting.
[0208] By the way, when a gray scale value specified in the image
data Da is p2 in the (X-1) frame, a gray scale voltage in the (X-1)
frame becomes P2 corresponding to the gray scale value p2,
regardless of variation of the gray scale voltages from the
previous (X-2) frame (not shown).
[0209] In the X frame, the gray scale value is varied from the gray
scale value p2 of the previous (X-1) frame to the gray scale value
r1. Here, since the negative polarity is designated, a relationship
of r1<p2 is established, and the gray scale voltages specified
in the image data Da decreases over the range from the (X-1) frame
to the X frame and a difference between the gray scale voltages is
negative. On this account, the voltage pattern selecting unit 15
selects the voltage pattern 92 belonging to the third pattern and
corresponding to the gray scale value r1. Accordingly, the image
data Db corresponding to the pixel becomes the gray scale voltage
P1 in the first and second fields of the x frame, the gray scale
voltage P2 in the subsequent third field, and again the gray scale
voltage P1 in the fourth field.
[0210] When the gray scale voltages are decreased in the X frame,
since the gray scale voltage P1 shifted in the decreasing direction
in the first and second fields is marked to the liquid crystal
capacitor of the pixel prior to a voltage corresponding to the gray
scale value r1 specified in the image data Da, it is possible to
improve the responsiveness of the liquid crystal 305 having a
relatively low response speed. In addition, the gray scale value r1
is located on a point at which a distance between the gray scale
value p1 and the gray scale value p2 is divided internally with a
ratio of 1:3, and the gray scale voltage P1 corresponding to the
gray scale value p1 is applied to the pixel electrode over the sum
of three fields of the first, second, and fourth fields, while the
gray scale voltage P2 corresponding to the gray scale value p2 is
applied to the pixel electrode only during the third field.
Accordingly, desired pseudo gray scale levels are almost
represented when one frame is viewed.
[0211] The gray scale value r1 of the (X+1) frame is not varied
from the previous x frame. On this account, the voltage pattern
selecting unit 15 selects the voltage pattern 72 belonging to the
first pattern and corresponding to the gray scale value r1.
Operation at this time is similar to the above-described operation
(FIG. 18B).
[0212] As described above, in the third embodiment, if the gray
scale values specified in the image data Da of the current frame do
not correspond to the outputtable voltage of the X driver 30, when
the gray scale values specified in the image data Da are varied to
become higher than the gray scale voltages of the previous frame,
the gray scale voltages shifted in the increasing direction to
become higher than the gray scale voltages specified in the image
data Da are controlled to be applied to the preceding first field.
If the gray scale values specified in the image data Da of the
current frame do not correspond to the outputtable voltage of the X
driver 30, when the gray scale values specified in the image data
Da are varied to become lower than the gray scale voltages of the
previous frame, the gray scale voltages shifted in the decreasing
direction to become lower than the gray scale voltages specified in
the image data Da are controlled to be applied to the preceding
first field.
[0213] Accordingly, according to the third embodiment, display
characteristics of the liquid crystal display panel 50 can be
improved and a response speed thereof can be increased.
[0214] In addition, in the third embodiment, since the liquid
crystal display panel 50 is driven with one frame divided into four
fields, it is possible to further improve the ability to represent
halftones.
[0215] In the third embodiment, the case where gray scale levels of
the gray scale values r1 are represented is described. However, the
same control may also be applied to a case where gray scale levels
of the gray scale values r2 and r3 are represented. More
specifically, when the gray scale levels of the gray scale value r2
(or r3) represented in the current frame, a voltage, which
corresponds to the gray scale value r2 (or r3), of the second
voltage pattern is used when the gray scale value r2 (or r3) is
varied to become increased from the gray scale voltage of the
previous frame, while a voltage, which corresponds to the gray
scale value r2 (or r3), of the third voltage pattern is used when
the gray scale value r2 (or r3) is varied to become decreased from
the gray scale voltage of the previous frame.
[0216] In addition, in the third embodiment, it is configured that
one of the second and third patterns is selected if the difference
between the gray scale voltages over the range from the previous
frame to the current frame. However, it may be configured that the
first pattern is selected if an absolute value of the difference is
smaller than the predetermined threshold, and one of the second and
third patterns is selected depending on a polarity (+ or -) if the
absolute value of the difference exceeds the predetermined
threshold.
[0217] In addition, in the third embodiment, when one frame is
divided into four fields, the scan lines are selected in order as
shown in FIG. 15. However, as shown in FIG. 12, the scan lines may
be selected in order as shown in FIG. 20.
Fourth Embodiment
[0218] In the first, second and third embodiments, it is configured
that the image data Db (voltage patterns) is generated (selected)
to make voltages to be applied to each fields different only when
the gray scale values specified in the image data Da of the current
frame do not correspond to the outputtable voltages of the X driver
30. However, in a fourth embodiment, it is configured that, even
when the gray scale values specified in the image data Da of the
current frame correspond to the outputtable voltages of the x
driver 30, a voltage pattern having different voltages of each
field is selected depending on variation of the gray scale voltages
over the range from the previous frame to the current frame.
[0219] More specifically, in the fourth embodiment, one frame is
divided into two fields, for example, like the second embodiment,
and the voltage pattern selecting unit 15 in the data processing
circuit 10 selects the first pattern if the difference between the
gray scale voltages over the range from the previous frame to the
current frame is 0, selects the second pattern if the difference is
positive (that is, the variation direction is the increasing
direction), and selects the third pattern if the difference is
negative (that is, the variation direction is the decreasing
direction), as shown in FIG. 14.
[0220] Next, in the fourth embodiment, marks obtainable when the
gray scale values or mark polarities of the pixels are varied from
an immediate previous frame will be considered.
[0221] FIG. 21A is a view illustrating variation of the gray scale
values specified in the image data Da of one pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0222] As shown in this drawing, the image data Da are input in
order of an (X-1) frame, an X frame and an (X+1) frame. More
specifically, the gray scale value u1 is specified in the (X-1)
frame and the gray scale value u2 is specified in the X frame and
the (X+1) frame. That is, the gray scale value is varied from the
gray scale value u1 to the gray scale value u2 over a range from
the (X-1) frame to the X frame, and the gray scale value u2 is
predetermined over a range from the X frame to the (X+1) frame.
[0223] In addition, both of the gray scale values u1 and u2 are
gray scale values corresponding to the outputtable voltages of the
X driver 30. In addition, a negative polarity is designated through
the (X-1) frame, the x frame and the (X+1) frame.
[0224] FIG. 21B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18), that is, a voltage applied to the
pixel electrode of the pixel to be considered, when the gray scale
values specified in the image data Da are varied as shown in FIG.
21A. In this drawing, a horizontal axis denotes time and a vertical
axis denotes a gray scale voltage.
[0225] When a gray scale value specified in the image data Da in
the (X-1) frame is u1, if there is no variation of the gray scale
voltages from the previous (X-2) frame (not shown), since the first
pattern is selected in the (X-1) frame, a gray scale voltage in the
(X-1) frame becomes U1 corresponding to the gray scale value u1
over a range from the first field to the third field.
[0226] The gray scale value u2 specified in the image data Da in
the X frame is increasing from the gray scale value u1 of the
previous (X-1) frame. Here, since the negative polarity is
designated, a relationship of u1<u2 is established. On the
account, since the gray scale voltages specified in the image data
Da increase over the range from the (X-1) frame to the X frame and
a difference between the gray scale voltages is positive, the
voltage pattern selecting unit 15 selects the second pattern.
Accordingly, the image data Db corresponding to the pixel becomes a
gray scale voltage U3 shifted in a voltage increasing direction,
rather than a gray scale voltage U2 corresponding to the gray scale
value u2, in the first field of the X frame and a gray scale
voltage U4 shifted in a voltage decreasing direction opposite to
the voltage increasing direction, rather than the gray scale
voltage U2, in the subsequent second field.
[0227] In addition, the gray scale voltages U3 and U4 are gray
scale voltages corresponding to adjacent gray scale values of the
gray scale value u2, for example, and have a relationship with the
gray scale voltage U2 corresponding to the gray scale value u2,
that is, an equation of U3>U2>U4.
[0228] The (X+1) frame has the same gray scale value u2 as the X
frame, and has the same gray scale voltage as the X frame since
both frames have the negative polarity, as described above.
[0229] On this account, since the voltage pattern selecting unit 15
selects the first pattern in the (X+1) frame, the image data Db
specifies the gray scale voltage U2 corresponding to the gray scale
value u2 in the first and second fields.
[0230] When corresponding scan lines in each field of one frame are
selected, the image data Db corresponding to the field is converted
to an analog signal by the X driver 30 and the analog signal is
applied to corresponding signal lines. Accordingly, the gray scale
voltages specified in the image data Db are applied to the pixel
electrode.
[0231] In this example, the case where the gray scale voltages
specified in the image data Da increase has been described. Now, a
case where the gray scale voltages specified in the image data Da
decrease will be considered.
[0232] FIG. 22A is a view illustrating variation of the gray scale
values specified in the image data Da of one pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0233] As shown in this drawing, the image data Da are input in
order of the (X-1) frame, the X frame and the (X+1) frame. More
specifically, the gray scale value u2 is specified in the (X-1)
frame and the gray scale value u1 is specified in the X frame and
the (X+1) frame. That is, the gray scale value is varied from the
gray scale value u2 to the gray scale value u1 over the range from
the (X-1) frame to the X frame, and the gray scale value u1 is
predetermined over the range from the X frame to the (X+1)
frame.
[0234] In addition, as described above, both of the gray scale
values u1 and u2 are gray scale values corresponding to the
outputtable voltages of the X driver 30. In addition, the negative
polarity is designated through the (X-1) frame, the X frame and the
(X+1) frame.
[0235] FIG. 22B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18), that is, a voltage applied to the
pixel electrode of the pixel to be considered, when the gray scale
values specified in the image data Da are varied as shown in FIG.
22A. In this drawing, a horizontal axis denotes time and a vertical
axis denotes a gray scale voltage.
[0236] When a gray scale value specified in the image data Da in
the (X-1) frame is u2, if there is no variation of the gray scale
voltages from the previous (X-2) frame (not shown), since the first
pattern is selected in the (X-1) frame, a gray scale voltage in the
(X-1) frame becomes U2 corresponding to the gray scale value u2
over the range from the first field to the third field.
[0237] The gray scale value u1 specified in the image data Da in
the X frame is decreasing from the gray scale value u2 of the
previous (X-1) frame. Here, since the negative polarity is
designated, a relationship of u1<u2 is established. On the
account, since the gray scale voltages specified in the image data
Da increase over the range from the (X-1) frame to the X frame and
a difference between the gray scale voltages is negative, the
voltage pattern selecting unit 15 selects the third pattern.
Accordingly, the image data Db corresponding to the pixel become a
gray scale voltage U5 shifted in a voltage decreasing direction,
rather than the gray scale voltage U1 corresponding to the gray
scale value u1, in the first field of the X frame and a gray scale
voltage U6 shifted in a voltage increasing direction opposite to
the voltage decreasing direction, rather than the gray scale
voltage U1, in the subsequent second field.
[0238] In addition, the gray scale voltages U5 and U6 are gray
scale voltages corresponding to adjacent gray scale values of the
gray scale value u1, for example, and have a relationship with the
gray scale voltage U1 corresponding to the gray scale value u1,
that is, a relationship of U5>U1>U6.
[0239] The (X+1) frame has the same gray scale value u1 as the X
frame, and has the same gray scale voltage as the X frame since
both frames have the negative polarity, as described above.
[0240] On this account, since the voltage pattern selecting unit 15
selects the first pattern in the (X+1) frame, the image data Db
specifies the gray scale voltage U1 corresponding to the gray scale
value u1 in the first and second fields.
[0241] In this manner, in the fourth embodiment, regardless of
whether or not the gray scale values specified in the image data Da
of the current frame are gray scale values corresponding to the
outputtable voltages of the X driver 30, the second pattern is
selected when the gray scale voltages specified in the image data
Da of the current frame increase from the previous frame and the
third pattern is selected when the gray scale voltages
decrease.
[0242] In this manner, in the fourth embodiment, when the gray
scale values specified in the image data Da in the current frame
are varied to become higher than the gray scale voltages of the
previous frame, the gray scale voltages shifted in the increasing
direction to become higher than the gray scale voltages specified
in the image data Da are controlled to be applied to the preceding
first field. On the other hand, when the gray scale values
specified in the image data Da of the current are varied to become
lower than the gray scale voltages of the previous frame, the gray
scale voltages shifted in the decreasing direction to become lower
than the gray scale voltages specified in the image data Da are
controlled to be applied to the preceding first field.
[0243] Accordingly, according to the fourth embodiment, display
characteristics of the liquid crystal display panel 50 can be
improved and a response speed thereof can be increased.
[0244] In the fourth embodiment, the case where one frame is
divided into two fields is described. However, the present
invention is applicable to a case where one frame is divided into
three fields or four fields, for example, instead of two
fields.
[0245] Now, a case where one frame is divided into three fields
will be described. Also in this case, the voltage pattern selecting
unit 15 of the data processing circuit 10 selects one of the first,
second and third patterns based on the amount of variation
(difference) of the gray scale voltages specified in the image data
Da over the range from the previous frame to the current frame.
[0246] However, when one frame is divided into three fields, that
is, first, second and third fields, the first, second and third
patterns are different from those shown in FIG. 12.
[0247] Although not shown particularly, in the first pattern
corresponding to no variation of the gray scale voltages, the gray
scale voltages specified in the image data Da of the current frame
are predetermined over the range from the first field to the third
field.
[0248] In addition, in the second pattern corresponding to the
increase of the gray scale voltages, a gray scale voltage in the
first field becomes higher than the gray scale voltages specified
in the image data Da of the current frame, a gray scale voltage in
the second field becomes lower than the gray scale voltages
specified in the image data Da of the current frame, and a gray
scale voltage in the third field becomes the gray scale voltage
specified in the image data Da of the current frame.
[0249] In addition, the second and third patterns have a
relationship that an average value of the gray scale voltages of
the first and second fields becomes a gray scale voltage of the
third field.
[0250] Next, in the fourth embodiment, when one frame is divided
into three fields, that is, the first, second and third fields,
marks obtainable when the gray scale values or mark polarities of
the pixels are varied from an immediate previous frame will be
considered.
[0251] FIG. 23A is a view illustrating variation of the gray scale
values specified in the image data Da of one pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0252] As shown in this drawing, the image data Da are input in
order of an (X-1) frame, an X frame and an (X+1) frame. More
specifically, the gray scale value u1 is specified in the (X-1)
frame and the gray scale value u2 is specified in the X frame and
the (X+1) frame. That is, the gray scale value is varied from the
gray scale value u1 to the gray scale value u2 over a range from
the (X-1) frame to the X frame, and the gray scale value u2 is
predetermined over a range from the X frame to the (X+1) frame.
[0253] In addition, both of the gray scale values u1 and u2 are
gray scale values corresponding to the outputtable voltages of the
X driver 30. In addition, a negative polarity is designated through
the (X-1) frame, the X frame and the (X+1) frame.
[0254] FIG. 23B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18), that is, a voltage applied to the
pixel electrode of the pixel to be considered, when the gray scale
values specified in the image data Da are varied as shown in FIG.
23A. In this drawing, a horizontal axis denotes time and a vertical
axis denotes a gray scale voltage.
[0255] When a gray scale value specified in the image data Da in
the (X-1) frame is u1, if there is no variation of the gray scale
voltages from the previous (X-2) frame (not shown), since the first
pattern is selected in the (X-1) frame, a gray scale voltage in the
(X-1) frame becomes U1 corresponding to the gray scale value u1
over a range from the first field to the third field.
[0256] The gray scale value u2 specified in the image data Da in
the X frame is increasing from the gray scale value u1 of the
previous (X-1) frame. Here, since the negative polarity is
designated, a relationship of u2>u1 is established. On the
account, since the gray scale voltages specified in the image data
Da increase over the range from the (X-1) frame to the X frame and
a difference between the gray scale voltages is positive, the
voltage pattern selecting unit 15 selects the second pattern.
Accordingly, the image data Db corresponding to the pixel becomes a
gray scale voltage U7 shifted in a voltage increasing direction,
rather than a gray scale voltage U2 corresponding to the gray scale
value u2, in the first field of the X frame, a gray scale voltage
U8 shifted in a voltage decreasing direction opposite to the
voltage increasing direction, rather than the gray scale voltage
U2, in the subsequent second field, and the gray scale voltage U2
corresponding to the gray scale value u2 in the subsequent third
field.
[0257] In addition, the gray scale voltages U7 and U8 are gray
scale voltages corresponding to adjacent gray scale values of the
gray scale value u2, for example, and have a relationship with the
gray scale voltage U2 corresponding to the gray scale value u2,
that is, a relationship of U7>U2>U8.
[0258] The (X+1) frame has the same gray scale value u2 as the X
frame, and has the same gray scale voltage as the X frame since
both frames have the negative polarity, as described.
[0259] On this account, since the voltage pattern selecting unit 15
selects the first pattern in the (X+1) frame, the image data Db
specifies the gray scale voltage U2 corresponding to the gray scale
value u2 in the first, second and third fields.
[0260] In addition, when corresponding scan lines in each field of
one frame are selected, the image data Db corresponding to the
field are converted to an analog signal by the x driver 30 and the
analog signal is applied to corresponding signal lines.
Accordingly, the gray scale voltages specified in the image data Db
are applied to the pixel electrode.
[0261] In this manner, according to the fourth embodiment, even
when one frame is divided into three fields and four or more
fields, display characteristics of the liquid crystal display panel
50 can be improved and a response speed thereof can be
increased.
Fifth Embodiment
[0262] In the above-described embodiments, for one pixel to be
considered, a voltage applied to the pixel electrode of the pixel
in each field of the current frame is determined depending on
variation of the gray scale voltages specified in the image data Da
over the range from the previous frame to the current frame. That
is, when two adjacent frames are considered, a voltage applied to
each field of a later frame is determined depending on variation of
a gray scale voltage from a previous frame.
[0263] However, the present invention is not limited to this
configuration. For example, it may be configured that, when two
adjacent frames are considered, a voltage applied in each field of
a previous frame is determined depending on variation of a gray
scale voltage to a later frame.
[0264] Now, a fifth embodiment employing such configuration will be
described. A frame later than the current frame to be processed is
called a `next frame`.
[0265] In the fifth embodiment, a voltage pattern of the current
frame is selected based on the image data Da of the current frame
and the next frame. More specifically, for example, the voltage
determining unit 18 of the data processing circuit 10 assumes image
data read from the frame memory 11 and delayed by one frame as the
image data of the current frame, assumes image data directly
supplied from the external super ordinate device as the image data
of the next frame, and selects a voltage pattern of the current
frame based on the image data of the current frame and the next
frame. Accordingly, in the fifth embodiment, a display delayed for
the image data supplied from the external super ordinate device is
achieved.
[0266] The reason for such configuration is to avoid inconsistency
in time by assuming the previous frame in the first to fourth
embodiments as the current frame in the fifth embodiment and
assuming the current frame in the first to fourth embodiments as
the next frame in the fifth embodiment because image data of the
next frame in future will not be supplied at a stage in which the
image data Da of the current frame is supplied.
[0267] In addition, when one frame is divided into two fields, that
is, the first and second fields, the first pattern is the same as
FIG. 14, but the second and third patterns are in a reverse
relationship with those shown in FIG. 14. That is, when the
variation direction of a gray scale voltage is the increasing
direction, the gray scale voltage becomes a voltage shifted in the
variation direction in the second field of the current frame and a
voltage shifted in a direction opposite to the variation direction
in the first field of the current frame, and the voltage of the
second field becomes higher than the voltage of the first field. On
the contrary, when the variation direction of the gray scale
voltage is the decreasing direction, the voltage of the second
field becomes lower than the voltage of the first field.
[0268] In addition, in the fifth embodiment, one frame is divided
into two fields, for example, like the second embodiment, and the
voltage pattern selecting unit 15 in the data processing circuit 10
selects the first pattern if the gray scale voltages specified in
the image data Da of the current frame are the outputtable voltages
of the X driver 30. In addition, if the gray scale voltages
specified in the image data Da of the current frame are not the
outputtable voltages of the X driver 30, the voltage pattern
selecting unit 15 selects the second pattern because of the image
data Db of the current frame if the difference between the gray
scale voltages over the range from the current frame to the next
frame is positive (that is, the variation direction is the
increasing direction) and selects the third pattern if the
difference is negative (that is, the variation direction is the
decreasing direction).
[0269] In addition, if the gray scale voltages decoded in the
decoder 12 are not the outputtable voltages of the X driver 30, the
voltage pattern selecting unit 15 again outputs the voltage pattern
selected in the previous frame and also in the current frame when
the difference between the gray scale voltages over the range from
the current frame to the next frame is 0.
[0270] Next, in the fifth embodiment, marks of voltages will be
considered.
[0271] FIG. 24A is a view illustrating variation of the gray scale
values specified in the image data Da of the pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0272] As shown in this drawing, the image data Da is input in
order of an (X-2) frame, an (X-1) frame, an X frame and an (X+1)
frame. More specifically, a gray scale value q1 is specified in the
(X-2) to X frames and a gray scale value p3 is specified in the
(X+1) frame. That is, the gray scale value is predetermined with
the gray scale value q1 in the (X-2) frame to the X frame, and the
gray scale value is varied from the gray scale value q1 to the gray
scale value p3 over the range from the X frame to the (X+1)
frame.
[0273] In addition, the gray scale values q1 is not a gray scale
value corresponding to the outputtable voltages of the X driver 30,
but the gray scale value p3 is a gray scale value corresponding to
the outputtable voltages of the X driver 30. In addition, a
negative polarity is designated through the (X-2) frame, the (X-1)
frame, the X frame and the (X+1) frame.
[0274] FIG. 24B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18), that is, a voltage applied to the
pixel electrode of the pixel to be considered, when the gray scale
values specified in the image data Da are varied as shown in FIG.
24A. In this drawing, a horizontal axis denotes time and a vertical
axis denotes a gray scale voltage.
[0275] When a pixel is considered, the gray scale value q1
specified in the image data Da in the (X-1) frame is not a gray
scale value corresponding to the outputtable voltages of the X
driver 30 and there is no variation of the gray scale voltages from
the (X-2) frame. On this account, the voltage pattern selecting
unit 15 again selects a voltage pattern of the (X-2) frame as a
voltage pattern of the (X-1) frame for the pixel. That is, the
image data Db corresponding to the pixel specify the gray scale
voltage P2 in the first field of the (X-1) frame and the gray scale
voltage P1 in the subsequent second field.
[0276] Here, the gray scale voltages P2 and P1 are gray scale
voltages corresponding to adjacent gray scale values of the gray
scale value q1, for example, and have a relationship with a
non-outputtable gray scale voltage Q1 of the X driver 30
corresponding to the gray scale value q1, that is, a relationship
of P1>Q1>P2.
[0277] The gray scale value specified in the image data Da
increases from q1 to p3 over the range from the X frame to the
(X+1) frame. Here, since the negative polarity is designated, a
relationship of q1<p3 is established. Accordingly, since the
gray scale voltage specified in the image data Da increases over
the range from the X frame to the (X+1) frame and a difference is
positive, the voltage pattern selecting unit 15 selects the second
pattern as the voltage pattern of the X frame for the pixel.
Accordingly, the image data Db corresponding to the pixel in the X
frame specifies the gray scale voltage P1 in the first field and
the gray scale voltage P2 in the second field, contrary to the
(X-1) frame.
[0278] If the gray scale value p3 specified in the image data Da in
the (X+1) frame is a gray scale value corresponding to the
outputtable voltages of the X driver 30 and there is no variation
of the gray scale voltage in an (X+2) frame (not shown), the
voltage pattern selecting unit 15 selects the first pattern as the
voltage pattern of the (X+1) frame for the pixel. Accordingly, the
image data Db corresponding to the pixel in the (X+1) frame specify
a gray scale voltage P3 corresponding to the gray scale value p3 in
the first and second fields.
[0279] In addition, when corresponding scan lines in each field of
one frame are selected, the image data Db corresponding to the
field is converted to an analog signal by the x driver 30 and the
analog signal is applied to corresponding signal lines.
Accordingly, the gray scale voltages specified in the image data Db
are applied to the pixel electrode.
[0280] In this example, the case where the gray scale voltages
specified in the image data Da increase has been described. Now,
the case where the gray scale voltages specified in the image data
Da decrease will be considered.
[0281] FIG. 25A is a view illustrating variation of the gray scale
values specified in the image data Da of the pixel to be
considered. In this drawing, a horizontal axis denotes time and a
vertical axis denotes a gray scale value.
[0282] As shown in this drawing, the image data Da is input in
order of the (X-2) frame, the (X-1) frame, the X frame and the
(X+1) frame. More specifically, the gray scale value p3 is
specified in the (X-2) to X frames and the gray scale value q1 is
specified in the (X+1) frame. That is, the gray scale value is
predetermined with the gray scale value p3 in the (X-2) frame to
the X frame, and the gray scale value is varied from the gray scale
value p3 to the gray scale value q1 over the range from the x frame
to the (X+1) frame.
[0283] In addition, the gray scale values p3 is not a gray scale
value corresponding to the outputtable voltages of the x driver 30,
but the gray scale value q1 is a gray scale value corresponding to
the outputtable voltages of the X driver 30. In addition, a
negative polarity is designated through the (X-2) frame, the (X-1)
frame, the X frame and the (X+1) frame.
[0284] FIG. 25B shows the gray scale voltages specified in the
image data Db output from the data processing circuit 10 (the
voltage determining unit 18), that is, a voltage applied to the
pixel electrode of the pixel to be considered, when the gray scale
values specified in the image data Da are varied as shown in FIG.
25A. In this drawing, a horizontal axis denotes time and a vertical
axis denotes a gray scale voltage.
[0285] When a pixel is considered, the gray scale value p3
specified in the image data Da in the (X-1) frame is not a gray
scale value corresponding to the outputtable voltages of the X
driver 30 and there is no variation of the gray scale voltages from
the (X-2) frame. On this account, the voltage pattern selecting
unit 15 again selects a voltage pattern of the (X-2) frame as a
voltage pattern of the (X-1) frame for the pixel. That is, the
image data Db corresponding to the pixel specify the gray scale
voltage P2 in the first field of the (X-1) frame and the gray scale
voltage P3 in the subsequent second field.
[0286] Here, the gray scale voltages P2 and P3 are gray scale
voltages corresponding to adjacent gray scale values of the gray
scale value q2, for example, and have a relationship with a
non-outputtable gray scale voltage Q2 of the X driver 30
corresponding to the gray scale value q2, that is, a relationship
of P2>Q2>P3.
[0287] The gray scale value specified in the image data Da
decreases from p3 to q1 over the range from the X frame to the
(X+1) frame. Here, since the negative polarity is designated, a
relationship of p3<q1 is established. Accordingly, since the
gray scale voltage specified in the image data Da decreases over
the range from the X frame to the (X+1) frame and a difference is
negative, the voltage pattern selecting unit 15 selects the third
pattern as the voltage pattern of the X frame for the pixel.
Accordingly, the image data Db corresponding to the pixel in the X
frame specifies the gray scale voltage P3 in the first field and
the gray scale voltage P2 in the second field, contrary to the
(X-1) frame.
[0288] If the gray scale value q1 specified in the image data Da in
the (X+1) frame is a gray scale value corresponding to the
outputtable voltages of the X driver 30 and there is no variation
of the gray scale voltage in an (X+2) frame (not shown), the
voltage pattern selecting unit 15 selects the first pattern as the
voltage pattern of the (X+1) frame for the pixel. Accordingly, the
image data Db corresponding to the pixel in the (X+1) frame specify
a gray scale voltage P1 corresponding to the gray scale value p1 in
the first and second fields.
[0289] In this manner, in the fifth embodiment, when the gray scale
voltages are varied over the range of the current frame to the next
frame, since a voltage shifted in a direction opposite to the
variation direction is marked on the liquid crystal capacitor in
the first field of the current frame and a voltage in the variation
direction is marked on the liquid crystal capacitor in the
subsequent second field, it is possible to improve the
responsiveness of the liquid crystal 305 having a relatively slow
response speed, as in the first to fourth embodiment. In addition,
in this embodiment, even when gray scale to be represented for one
frame corresponds to a non-outputtable voltage of the X driver 30,
since the gray scale includes pseudo gray scale values represented
in the first and second fields using the gray scale values
corresponding to the outputtable voltages of the X driver 30, it is
possible to increase the number of representable gray scale
levels.
Applications and Modifications
[0290] In the above embodiments, in fields into which one frame is
divided, the gray scale voltages having a difference at a high
level or a low level with respect to the voltage LCcom of the
common electrode 308 depending on the gray scale values of a pixel
to be considered are applied to the signal lines corresponding to
the pixel. However, the present invention is not limited to this.
For example, it is sufficient if the liquid crystal capacitor 320
maintains an effective voltage according to gray scale values on a
per-field basis. Accordingly, for example, it may be configured
that pulse signals having a width according to gray scale values
are applied to the signal lines corresponding to the pixel.
[0291] When the pulse signals having the width according to the
gray scale values are applied to the signal lines, the pixels 300
will be here described by way of example of the configuration shown
in FIG. 2B although they may have the configuration shown in FIG.
2A.
[0292] FIG. 2B is a view illustrating configuration of four
(2.times.2) pixels formed at intersections of an i-th row, an
adjacent (i+1)-th row, a j-th column, and an adjacent (j+1)-th
column.
[0293] As shown in this drawing, each of the pixels 300 which are
arranged at intersections of scan lines G.sub.i and G.sub.(i+1) and
signal lines S.sub.j and S.sub.(j+1), includes a liquid crystal
capacitor 320 and a thin film diode (TFD) 317 connected in
series.
[0294] Here, for example, a TFD 317 of a pixel 300 at the i-th row
and j-th column is turned on when the scan line G.sub.i at the i-th
row is applied with a select voltage, regardless of a voltage of a
data signal supplied to the signal line S.sub.j at the j-th column,
while being turned off when the scan line G.sub.i is applied with a
non-select voltage. A liquid crystal capacitor 320 at the i-th row
and j-th column has one electrode connected to the signal line
S.sub.j at the j-th column and the other electrode 318 connected to
the pixel electrode connected to the TFD 317, with the liquid
crystal 305 interposed between both electrodes, and has
transmittance (or reflectivity) depending on an effective voltage
across both electrodes.
[0295] Accordingly, even though only signal lines at the j-th and
(j+1)-th columns are shown in FIG. 2B, signal lines at each column
are formed in a stripe shape such that the signal lines are
opposite to the pixel electrodes 318 of the pixels 300 at one
column.
[0296] Accordingly, for the 480.times.640 pixels 300, for example,
it is configured such that the scan lines are selected sequentially
and select voltages +Vs and -Vs are alternately applied to the
selected scan lines, as shown in FIG. 26, while pulse signals
having a width according to the gray scale values are supplied via
the scan lines, as shown in FIG. 27. In this configuration, the
TFDs 317 of the pixels 300 at one row, which are located on scan
lines having the select voltage +Vs or -Vs, are turned on and a
voltage difference between the select voltage and a voltage of the
pulse signal applied to the scan lines are maintained in the liquid
crystal capacitor 320. Even when a scan signal has a non-select
voltage +Vd or -Vd to turn off the TFDs 317, the liquid crystal
capacitor 320 maintains a voltage when the TFDs 317 are turned on.
Accordingly, when the select voltages are applied to the scan
lines, the pixels 300 can be displayed with brightness according to
the gray scale values by specifying the width of the pulses
supplied to the signal lines according to the gray scale values
while specifying polarity of the pulses according to polarity of
the select voltages.
[0297] As shown in FIG. 27, a pulse signal supplied to the signal
lines has one of the voltages +Vd and -Vd.
[0298] Considering the pixel 300 at the i-th row and j-th column,
when the scan line G.sub.i at the i-th row has a positive select
voltage +Vs, a negative voltage -Vd increases the effective voltage
maintained in the liquid crystal capacitor 320. Accordingly, for
the pixel 300 at the i-th row and j-th column, when a gray scale
value for each field of the current frame is determined using image
data of the current frame and image data of the previous (or next)
frame, a pulse having the voltage -Vd prolonged as the gray scale
value corresponding to the field becomes small in an interval
during which the positive select voltage +Vs is applied is
preferably supplied to the signal line S.sub.j at the j-th
column.
[0299] On the other hand, when the scan line G.sub.i at the i-th
row has a negative select voltage -Vs, a positive voltage +Vd
increases the effective voltage maintained in the liquid crystal
capacitor 320. Accordingly, for the pixel 300 at the i-th row and
j-th column, when a gray scale value for each field of the current
frame is determined by using image data of the current frame and
image data of the previous (or next) frame, a pulse having the
voltage +Vd prolonged as the gray scale value corresponding to the
field becomes small in an interval during which the negative select
voltage -Vs is applied is preferably supplied to the signal line
S.sub.j at the j-th column.
[0300] In the first to fifth embodiments, the gray scale voltage
applied to the pixel electrode is a voltage shifted to a high or
low level with respect to the voltage LCcom of the common electrode
308 depending on the gray scale values and includes information on
the mark polarity. Accordingly, the width of the pulse signal can
be specified by extracting the gray scale values from this
information, and a polarity of the pulse signal is preferably a
polarity opposite to a polarity of the select voltage applied to
the scan lines.
[0301] In addition, a reference of the above-mentioned polarity is
a potential Vc located at the center of the voltages +Vs and -Vs
(+Vd and -Vd), unlike the above-described first to fifth
embodiments. In addition, even though it is shown in FIG. 27 that a
voltage component of the pulse increasing the effective voltage
maintained in the liquid crystal capacitor 320 is in the later part
in an interval during which the select voltages are applied to the
scan lines, this voltage component may be in the former part in the
interval.
[0302] In addition, FIG. 26 shows an example of polarity reversion
every two frames for the liquid crystal capacitor 320. In addition,
FIG. 27 shows only representative gray scale values (gray scale
values corresponding to width of pulses outputtable from the X
driver 30).
[0303] In addition, the present invention is not limited to the use
of three voltage patterns (first, second and third patterns). For
example, it may be preferable that the number of voltage patterns
according to the number of fields into which one frame is divided
is prepared in advance and a voltage pattern is determined
depending on variation of gray scale voltages.
[0304] Alternatively, it may be configured that only one basic
voltage pattern is stored. More specifically, when one voltage
pattern is stored, it may be configured that re-adjustment
information used to re-adjust voltages is stored in correspondence
to variation of voltage gray scale values, the re-adjustment
information corresponding to the variation of the voltage gray
scale values specified by the image data of the previous and
current (next) frames is read, and gray scale voltages specified in
fields for the voltage patterns are altered based on the read
re-adjustment information.
[0305] Further, the present invention is not limited to the liquid
crystal display device, and is applicable to various kinds of
electro-optical devices such as electronic paper.
[0306] The entire disclosure of Japanese Patent Application Nos:
2005-083382, filed Mar. 23, 2005 and 2005-273405, filed Sep. 21,
2005 are expressly incorporated by reference herein.
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